The wide application of internet technology has provided the possibility to study and research new writing concepts and teaching modes in the classroom of English as a Second Language(ESL).In this trend,using email to assist English writing class has gained much attention in this field.This paper discusses the evaluation of email effectiveness with the implication of the Second Language Acquisition(SLA) theory.The result shows that the email assisted English writing class is a very salient method though it had its limitation somehow.