Abstract: The total supply capability (TSC) model fully studied the power supply capability of the existing distribution system, which is suitable to planning future power distribution systems and evaluating existed distribution systems. In this paper, the existing TSC model is improved, and a residue supply capability (RSC) calculation method which is more suitable to guide the operation of smart distribution network is presented. Firstly, the TSC model and related definitions are briefly introduced. Secondly, the concept of RSC is defined, the mathematical model of RSC is modified, and the solution method is given. Thirdly, the characteristics of the RSC are introduced, which shows that RSC is more suitable to guide the operation of distribution network. Finally, examples are given to illustrate the practicability and correctness of the proposed model. In this paper, the definition of RSC is defined, relative calculation algorithm is given, and the theoretical system of power supply capability is completed, which shows that it is more suitable for guiding the operation of distribution network, is conducive to the efficient usage of the power supply potential, and improves asset utilization.