By means of matching filling of five kinds of spherical silica with the particle size of 2μm, 3μm, 5μm, 10μm, 20μm respectively, the epoxy molding compounds(EMC) for integrated circuits(IC) were manufactured. Using classical particle accumulation theory, the particle distribution according with Dinger-Funk-Alfred equation was calculated by Matlab simulation software, and then the optimal particle size formulations were obtained. Adding the mixed silica according to the above optimal formulations into epoxy resin, the EMCs were manufactured by twin-roll compounding at 95~105°С . The melt viscosities of varied EMCs were measured by Rotating Rheometer. The results showed that the matching filling of different silica with different particle size can improve the flowability of EMC greatly.