The problem of fault current suppression is one of the main factors hindering the development of flexible high voltage direct current. The fault current is mainly affected by the DC power flow on the DC line. However, once the DC system breaks and leads to large-scale power flow transfer, the fault current suppression will be greatly challenged. In order to optimize the power flow transfer characteristics of a DC system, this paper takes the power flow distribution entropy and power flow transfer entropy as the indices to describe the power flow transfer characteristics of a DC system. Combined with the economic cost, a comprehensive index is constructed by weight as the optimization objective function of a particle swarm optimization algorithm, so as to find the optimal grid structure of the DC system considering the economic cost of power flow transfer characteristics. Compared with other types of grid structure DC systems, the proposed optimization method can improve the power flow transfer characteristics and control the economic cost. This work is supported by the National Key Research and Development Program of China (No. 2018YFB0904600).