The construction of new power system makes the structure of distribution network more and more complicated. Accurate power flow calculation can make the line loss management more efficient. This paper presents a new method for calculating the unbalanced power flow of distribution network. Firstly, the phase sequence of each node is determined by neural network identification, and then the three-phase unbalanced power flow is calculated by push-back method. The advantage of this method is that it can calculate the three-phase unbalanced power flow more accurately and quickly, and it can reduce the computational complexity and improve the computational efficiency. Finally, a distribution network example from Jiangxi Province is used to verify the feasibility and effectiveness of the proposed method.