The soap-free copolymer micro emulsion solutions of methyl methacrylate(MAA), n-butyl arcylate(BA), divinylbenzene and acrylic acid(AA) were prepared by employing potassium salt of maleic anhydride lauryl alcohol monoester as reactive emulsifier, n-amyl alcohol(PA) as co-surfactant and ammonium persulfate(ASP) as free-radical initiator at 75℃. The synthesis condition of reactive emulsifier- potassium salt of maleic anhydride lauryl alcohol monoester was optimized via orthogonal test. Using reactive emulsifier as a substitute for conventional emulsifier, the fatliquoring-retanning agent with a reinforcing effect was synthesized by micro emulsion copolymerization. The experimental product was used in retanning chrome tanned pigskin splits. The effect of the product was observed by measuring leather´s tensile strength, tearing strength and bursting strength. The result showed when the reactive emulsifier and monomer mixture(n-butyl arcylate(BA), methyl methacrylate(MAA) and divinylbenzene) was 120g and 180g, respectively, and the active monomer- acrylic acid was 10g, the retanning effect was best. In addition, the mechanical property of leather was highly improved, the horizontal tear strength was improved by 58.8%, while longitudinal tear strength was improved by 37.4%, and burst strength was improved by 54.1 %.