Water-soluble dietary fiber is significant to physiological function,while proportion of soluble dietary fiber is very small in raw resource,which cannot reach to the remand of the balance of dietary.Recently,many researchers study on the modification of dietary fiber by diverse methods.Using lemon peel as the raw material,we prepared lemon peel dietary fiber by Trichoderma Vitride fermentation or chemical method,the optimum conditions were determined by orthogonal design test.The result of orthogonal experiment indicated that the optimum conditions for extraction of dietary fiber from lemon peel by Trichoderma Viride were:fermentation temperature 32℃,fermentation time 72h and initial pH6.3.