Abstract: In order to prevent nano-particle aggregating,the nano-Al₂O₃ particle was prepared with PS by emulsion polymerization.In the emulsion polymerization,the effect of preparation conditions is studied,and the composite nanoparticles are characterizaed by means of TEM and FTIR.The results indicate the composite particles are approximately ball in shape and the particle consists of centered core(Al₂O₃) and outer shell(PS) and the shell thickness is about 10～20nm,when the reaction temperature is 800C,the preferable emulsifier system is the composite emulsifier of sodium lauryl sluphate and OP-10,the ratio of m(st):m(nano-Al₂O₃) is 2:1 and the velocity of dropping is 5 drops/min.