This paper discusses about both the effect of interfacial thermal barrier resistance and the effect of particle shape on the thermal conductivity of aluminum nitride powder filled polyimide (AlN/PI) composites. The interfacial thermal barrier resistance exhibits a negative effect on the thermal conductivity of AlN/PI composites. The shape of AlN particles exhibits a remarkable positive effect on the thermal conductivity of AlN/PI composites. A new modified equation, considering the both effects, for predicting the effective thermal conductivity of the composites is proposed. Several theoretical curves are compared with the experimental data. The result shows that the new modified equation is reasonable, and fit better than any other equations.