With the increasing application of renewable energy and energy storage in the distribution network, there is an urgent need to carry out research on the expansion planning of the distribution network that takes into account the uncertainties of the source and load ends. This paper proposes a threelevel distribution network expansion planning process and a random expected value model for distribution network expansion planning. Firstly, a network framework expansion planning model is established with comprehensive new cost as the optimization goal, connectivity, reliability, and power flow restrictions as constraints. As a result, the planned access plan and energy storage configuration capacity for the new site are determined. Secondly, the operation optimization model is established to calculate reasonable switch combination in normal operation mode. Finally partial reinforcement measures are adopted to improve system reliability. The validity of the model is verified in a practical system example.