The invention discloses a fault diagnosis method of a power distribution network in a power distribution system. The method includes the steps that a communication network is constructed by using distribution network management devices in the power distribution network as joints, and the distribution network management devices in the communication network can share monitoring data collected by the distribution network management devices, wherein the monitoring data includes corresponding identification of the distribution network management devices; the upstream and downstream relationships of the distribution network management devices in the power distribution network are determined according to current characteristics; according to change characteristics of the monitoring data of the distribution network management devices and the upstream and downstream position relationships of the distribution network management devices in the power distribution network, a fault report is generated, wherein the fault report includes one of or any combination of a fault position, a fault range and a fault type. By means of the method, the fault position and the fault type of the power distribution network can be automatically determined, man-made misjudgment can be effectively avoided, and the accuracy of fault judgment is further improved.