Nowadays it is the primary objective to improve energy efficiency of distribution network planning. However, it is focused on economic efficiency by most traditional models of distribution network planning. Therefore, a model of distribution network planning for optimal energy efficiency in power system is proposed. On the basis of the data for coal consumption, the factors are discussed such as the power loss of distribution network and the planning of distributed enregy, and these factors reflect comprehensively the energy efficiency of distribution network system. An improved algorithm of particle swarm optimization (POS) is used for the solution process in the proposed model by adding inertia weights, and this algorithm improves the convergence speed the accuracy at the same time. A radiation network shape strategy is also carried out to correct results individually. IEEE 33-bus examples are selected for verification. The calculation results show that the model with fast convergence and high stability, effectively improves the energy efficiency level of the distribution system, and it makes sure that the results of distribution network planning are reasonable. The present method is verified for its effectiveness of distribution network planning.