Block copolymer consists of two and more than two of different polymer links. Epoxy terminated polydtyrene (Ps-ep) active polymer was used to polymerize polystyrene (Pst)-polyethylene oxide (Peo) block copolymer P (st-b-eo). There were the mixtures of (Ps-ep), (Pst), (Peo) and P (st-b-eo) in the polymerization. It is necessary to separate (Ps-ep), (Pst), (Peo) and P (st-b-eo) in the mixtures in order to determine structure parameters of P (st-b-eo) block copolymers. We can know for certain their types of ABA, BAB and AB of polystyrene (A)-Polyethylene oxides (B) block copolymers with analysis of gel permeation chromatography (GPC).