Abstract: With the increase of distributed generator（DG） penetration rates, the research on the impact of DG on the methods and results of distribution network planning has become more and more practical. A simplified optimization model for the number of substations and feeders with DGs is established by using a probabilistic planning method. The objective of the model is to minimize the related total cost of substations and medium-voltage lines, and the line capacity constraints are considered. An approximate calculation model of the length of medium-voltage trunk lines and branch lines is proposed, and the influence of load variation, DG randomness and line load transfer rate on the outage time and outage cost is considered. Based on the minimum total cost and the optimized number of substations and feeders obtained by model solution, three categories of credit variables are defined. The examples show the significance of probabilistic planning for the selection of the number of substations and feeders, and the substitution effects of DGs.