Guided by educational policy of China,the authors of the present paper designed this study based on post-method theory.Theoritical reasons about application of E-mail in College English teaching are analyzed;functions and significance of this new kind of teaching mode are summerized;and how to use E-mail in and after class is also designed in detail.A practical research on how to use E-mail in writing teaching of College English was made on 85 freshmen(divided into experimental class and control class)from a university of Shanghai.Research results show that application of E-mail in writing teaching of College English is feasible,and the effect of the experimental class is obviously better than that of the control class taught in the traditional way.Their writing ability,comprehensive ability of English and communicating ability in English are all improved to a great extent.