Surface modification of silicon power is an efficient approach to improve the dispersion and compatibility of silicon in epoxy matrix. FT-IR and EDX analyses show that silane coupling agent had been grafted on the surface of silicon. The coefficient of thermal expansion of epoxy encapsulant had changed from 83.9×10^-6/K to 41.8×10^-6/K,decreasing approximately 50.1%.An optimization of workmanship had been done and showed as following: operating temperature is 60℃ and operating-time is up to 3h;curing program is 65℃/2h+105℃/4h+135℃/2h.