C language procedure is totally made up of function. Except main f unction (main function) that procedure must include and language storehouse func tion that itself offers, users can also define a lot of one's own function acco rding to their needs. Transfer other function through main function (the functio n of the storehouse , user's self-defining function), transferring each other b etween other functions, finish the corresponding procedure function. C language procedure is generally by a large amount of small function instead of forming by a small amount of great function, can let every part sufficient independence ea ch other so, and the task is single . The mistake apt to appear has been analyze d at the time of the application of function in C language in this article.