Abstract: In order to prevent nano-particle aggregating , the nano-Al₂O₃ particle was covered with PS by emulsionpolymerization. The st ructure of the emulsion polymeric Al₂O₃ / PS composite particle was characterized by TEMand FTIR. The result s indicate that the Al₂O₃ / PS composite particles take an approximate ball shape and the particle consist s of centered core (Al₂O₃ ) and outer shell ( PS) , and the shell thickness is about 10～20nm. The st ructureof polystyrene modified by Al₂O₃ / PS composite particles af ter SLS was studied by SEM and FE-SEM , respectively.It is found that the nano2particles disperse in the mat rix well , and the interfacial compatibility and adhesion propertyare improved , and the density of the sintering body is increased.