Abstract: Optimization of satellite power system topologies is an important way for reducing the weight.In terms of the sun synchronous orbit satellite,the energy transferring charts of four typical Direct Energy Transferring(DET)power systems are developed and the energy balance equations are derived.The optimal model is built up via minimizing the weight power ratio,which is based on the energy balance equations.An optimal analysis for the four kinds of DET power system topology is performed by taking the Descending Node Local Time,the ratio of the loads' peak energy consumption and long term energy consumption,the loads' power ratio in the orbit day and night as the design variables.An examples is calculated and the conclusions of the optimization are drawn.