The traditional distribution network power supply capacity evaluation is generally a single voltage level distribution network. As the distribution system covers multiple voltage levels, it cannot evaluate the entire distribution system comprehensively. In order to improve the limitation of the traditional method on the evaluation of the overall distribution capacity of the distribution network, based on the premise that distribution network has multiple voltage levels, a method and index for evaluating the inter - layer power supply capability of distribution network are proposed. Its significance is to evaluate the matching degree between superior and subordinate of distribution network under different voltage levels, it can take full account of the constraints between superior distribution network to the subordinate distribution network and the subordinate distribution network to the superior distribution network, and then evaluate the power supply capability of distribution network in all directions. According to the index of power supply margin and load capacity margin, the linear programming algorithm is used to establish the model, which can be used to judge the power supply capability of distribution network. Finally, the feasibility of the model is proved by the example analysis, so as to improve the index system to evaluate the maximum power supply capacity of distribution network.