Aluminum base composites with particles reinforced have high thermal conductivity, low thermal expansion coefficient, low density, and excellent working ability. On one hand the Sip/Al composites are prepared by pressure-less infiltration in experiments and take advantage of the finite element analysis to establish the models of Sip/Al composites. On the other hand, the Sip/Al composites morphology, the particles size, the volume fraction and the ratio between different Si particles have been discussed in the experiments. In experiments how they affect the thermal conductivity of the composites also has been explained. The thermal conductivity of Sip/Al composites is around 100 W/(m.k) at 50°C. When the Si volume fraction is definite, the thermal conductivity of the composites is little affected by the morphology, the size and the ratio between different Si particles. The study also showed that with the element Si content increasing, the thermal conductivity will decrease.