Abstract: RSA (random sequential adsorption) method was used to generate the representative volume element models of syntactic foams. Finite element software ANSYS was adopted to analyze the thermal expansion of syntactic foams. The relationships of thermal expansion coefficient of HGMs/resin and hollow glass microballoons (HGMs) filling ratio, coefficient of thermal expansion and HGMs wall-thickness were obtained. The two relation curves were fitted to linear function, and exponential function respectively, with the purpose of analyzing the sensitivity of the HGMs filling volume fraction and wall-thickness to the coefficient of thermal expansion. The stress fields and displacement fields caused by temperature load were also obtained. The results show that both of the increase of HGMs filling volume fraction and wall-thickness can reduce the coefficient of thermal expansion of HGMs/resin syntactic foams, and HGMs filling volume fraction shows the higher sensitivity than that of wall-thickness.