Introduction 
English grammar is a description of the usages of the English language by good speakers and writers of the present day. –Whitney
A description of account of the nature, build, constitution, or make of a language is called its grammar –Meiklejohn
Grammar teaches the laws of language, and the right method of using it in speaking and writing. –Patterson
Grammar is the science of letter; hence the science of using words correctly. –Abbott
The English word grammar relates only to the laws which govern the significant forms of words, and the construction of the sentence. -Richard Grant White
English grammar is the science which treats of the nature of words, their forms, and their uses and relations in the sentence.

Conception of grammar
Grammar is often misunderstood in the learning language. The misconception lies in the view that grammar is a collection of arbitrary rules about static structures in the language. Further questionable claims are that the structures do not have to be thought, learners will acquire them on their own, or if the structures are taught, the lessons that ensue will be boring. This thesis on comparative approach tries to make a brief analysis of necessity of grammar learning before it gives a relatively objective description of its function and significance in language learning. It argues that, grammar teaching is necessary in learning language.

Necessity of Grammar
Grammar learning is essential in learning language. Grammar rules like the molds of the parts of a machine, without them, workers can only stand by the iron—water. Similarly, English language learners who have been lacking in grammar rules instruction can neither use English language accurately to make a complete sentence, nor speak English language fluently on accuracy.

 
Necessity of grammar learning
It is exact that putting grammar in the foreground in second language teaching, because language knowledge of grammar and vocabulary is the base of English language. Grammatical competence is one of communicative competence. Communicative competence involves knowing how to use the grammar and vocabulary of the language to achieve communicative goals, and knowing how to do this in a socially appropriate way. Communicative goals are the goals of learners’ studying English language. So grammar teaching is necessary to achieve the goals. 

Grammar is not acquired naturally; it needs be taught
 It is true that some learners acquire second language grammar naturally without instruction. For example, there are immigrants to the United States who acquire proficiency in English on their own. This is especially true of young immigrants. However, this is not true for all learners, particularly the learners in China. We have no English surroundings. It is very difficult that studying English on our own. Though highly motivated learners with a particular aptitude for languages may achieve a degree of proficiency without any formal instruction, but whose English is far from accurate. An important question is that it is possible with grammar instruction to help learners who cannot achieve accuracy in English on their own

Grammar is not a collection of arbitrary rules 
Some people think that grammar is a collection of arbitrary rules. In fact it is not. While there is some synchronic Arbitrariness to grammar, not all of what is deemed arbitrary is so. If one adopts a broad enough perspective, it isPossible to see why things are the way they are. For example, the following sentences:
 (3) There is the book missing.
(4) There is a book missing.

Grammar books will say that sentence (3) is ungrammatical because sentences with existential there almost always take an indefinite noun phrase in the predicate. Why? The reason is not arbitrary. There used to introduce new information, and the preferred position for new information is toward the end of a sentence. A noun phrase that contains new information is marked by the use of the indefinite article, a or an, if it is a singular common noun, as in sentence

Grammar is the sentence—making machine
Part of process of language learning must be what is sometimes called item-learning ------that is the memorization of individual items such as words and phrases. However, there is a limit to the number of items a person can both retain and retrieve. Even travelers’ phrase books have limited usefulness-good for a three-week holiday, but there comes a point where we need to learn some pattern s or rules to enable us to generate new sentence. That is to say, it is grammar. Grammar, after all, is a description of the regularities in a language, and knowledge of these regularities provides the learner with the means to generate a potentially enormous number of original sentences. The number of possible new sentences is constrained only by the vocabulary at the learner’s command and his or her creativity. Grammar is a kind of ‘sentence-making machine’. It follows that the teaching of grammar offers the learner the means for potentially limitless linguistic creativity.

Grammar teaching is the rule-of-law
Grammar is a system of learnable rules; it lends itself to a view of teaching and learning known as transmission. A transmission view sees the role of education as the transfer of a body of knowledge from those that have the knowledge to those that do not. Such a view is typically associated with the kind of institutionalized learning where rules, order, and discipline are highly valued.

Conclusion 
The value of grammar teaching is important in English language teaching field. Grammar is the base of English language. It is not acquired naturally, but learning, it needs be instructed. Grammar operates at the sentence level and governs the syntax or word orders that are permissible in the language. It also works at the sub sentence level to govern such things as number and person agreement between subject and verb in a sentence. To grammar learning, some students may have a more analytical learning style than others, but if one hope to use English language accurately and fluently, it is necessary for him to receive grammar rules instruction. Grammar is not different from anything else; it is likely that students will learn at different rates. In a short word, grammar teaching is necessary in English language teaching.