With multiple emulsifier(SDS/SDBS) as initiators,St/BA microemulsion polymerization was initiated by the water-soluble potassium persulfate(KPS),oil-soluble benzoyl peroxide(BPO) and potassium persulfate/sodium sulfite(OR),and the behaviors of microemulsion polymerization were investigated. St/BA copolymer chemical composition and copolymer composition curves were obtained from Fourier infrared spectrums,and reactivity ratio of St/BA microemulsion polymerization initiated by three kinds of initiators were calculated.