Abstract: Based on the definition of 2-years impact factors,a formula between impact factor and self-citation year distribution coefficient was deduced.Citation literature distribution in different years is random and the peak can occur in 2 year impact factor calculation period,so the apparent its-citation impact factor(IF·YO)could not eliminate reasonably the interference of self-citation.A sample survey of 20 kinds of publications shows that rank ordering of apparent its-citation impact factor does not accord with that of its-citation impact factor(without self-citation),so the above theory is correct.It is proposed that the self-citation half-life index or citation distribution coefficient should be added in JCR at home and abroad in order to enhance objectivity and impartiality of periodical evaluation