Abstract: In order to meet the requirements for computational accuracy and efficiency of three-phase power flow of distribution network, this paper proposes a model and algorithm for single-three phase hybrid power flow calculation of distribution network. Firstly, the calculation model of three-phase power flow is deduced. Then, considering the uncertainties of distribution network, the three-phase model is used for the part where significant unbalance exists, while the single-phase model is used for the part where unbalance is negligible. These two parts of network are interconnected through a single-three phase interface, realizing the unified modelling for the single-phase network and the three-phase network. Finally, the location of the interface between the single and three-phase parts is automatically determined based on the unbalanced degree of line current. The case study result has verified the feasibility and efficiency of the proposed single-three phase hybrid power flow calculation method and the dynamic selection strategy of interfaces.