This work is one of the series，which studies the lepton identification in the BES (Beijing Spectrometer) in detail. The preliminary M.C. results about the discrimination between muon，electron and the other secondaries generated by hadron punch-through，especially by pion，are reported. The results show that there are two efficient cuts，i.e. the total charge Q and the second moment S for the discriminating of electron and pionin barrel shower counter，and there are also two cuts，i.e. position for direction for the discriminating of muon and pion in muon-system of BES. Thus the BES is of the good ability for the lepton identification.