There can be problems of waste of investment and low equipment utilization in traditional substation planning. To help solve these problems a full life cycle cost model for substation location and capacity is constructed. We take the confidence capacity evaluation method of distributed power sources and the capacity of substations, and the traditional substation planning method based on the weighted Voronoi diagram. From this we develop an optimized planning method for large-scale access of distributed power sources to substations. The validity and practicability of the proposed method are verified by calculation examples. Experiments show that the proposed method can effectively reduce the planned capacity of the power grid, improve the level of refinement of the power grid, and has good practicability. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. J2018063).