The increased penetration of distributed generation such as wind and light in the distribution grid causes dramatic fluctuations in net load, resulting in a sharp increase in the need for distribution grid flexibility. To this end, a distribution grid energy storage optimal allocation method considering source-net-load flexibility resources is proposed. First, a set of uncertain operation scenarios is established from multiple time scales using the K-means method and robust optimization theory; second, an economically flexible multi-objective optimization model with the minimum annual integrated cost and the highest average daily flexibility level of the distribution network as the optimization objectives is established and solved by a multi-objective composite differential evolutionary algorithm with embedded tide calculation. Arithmetic design and simulation are based on the IEEE 33-node distribution network system. The results validate the reasonableness and effectiveness of the proposed model considering source-grid-load flexibility resources in solving the energy storage allocation scheme.