The invention relates to a method and system for judging power flow direction of a power distribution network; the reference direction (positive direction) of the power flow is determined according toa voltage and current phase relation of each monitoring node, the reference direction is bound with the topological relation of the network; then, the power flow direction is judged according to thecomparison with the voltage and current phase relation of the reference power flow direction; if the phase relation between the voltage and current is consistent with the phase relation of the reference power flow direction, the power flow direction is a positive direction; otherwise, the power flow direction is a reverse direction. The method provided by the invention can be applied to judgementof power flow direction of open-loop and closed-loop power distribution networks. According to the technical scheme provided by the invention, the reference power flow direction is determined throughthe voltage and current phase relation and is bound with network topology, in actual operation, the actual power flow direction is judged according to the comparison with the voltage and current phaserelation specified by the reference power flow direction, the method is simple and rapid, the power flow direction is associated with the network topology, and the result is visual and clear.