Styrene (St) as hard monomer, butyl acrylate （BA）as soft monomer, N-Methylolacrylamide (N-MAM) as functional monomer, styrene/acrylic latexes was synthesized by semicontinuous emulsion polymerization. The performances of emulsion and impregnated auto-industry filter paper were examined and analyzed. The optimal condition of synthesizing emulsion was gained as that the best monomer compound of ST: BA was 0.49, the emulsifier’s dosage was 0.93%, the initiator’s dosage was 0.63%, the N-MAM’s dosage was 5.3%.The latex’s average particle diameter was 50nm and distributed equally. The performance indexes of impregnated filter paper were greater than 350kPa of bursting strength, more than 99min of water resistant property, over than 520L?m-2?s-1 of air permeability and at least 4.03 mN.m stiffness.