With the increasing scale of power system，the requirements for the distribution network are constantly increasing， and the power flow calculation of distribution network has become a hot research topic． Aiming at the limitations of the traditional forward/ backward substitution method，some improvements are proposed． Firstly，the ordinary method must number the nodes according to the certain requirements before performing the iterative calculation，but the improved one can omit this step by forming three matrices． Secondly，converting the transformer load to the high voltage side can make the distribution network a simple one － line diagram，thereby reducing the system scale． In addition，replacing the node injection power with the node injection current can save the branch loss calculation time ． Finally ，the reactive power correction equation of PV node can effectively process the distribution network with PV nodes，which solves the problem that the original method can not handle the PV nodes in distribution network system． The validity and feasibility of the proposed method are verified by the comparative simulations on IEEE 33 bus distribution network system and a 10 kV system with PV nodes．