Distribution network is the place with the most short circuit faults and low degree of intelligence. At present, the zero sequence current amplitude comparison method was mainly used for fault diagnosis of grounding fault, but there are some problems such as low recognition rate of non grounding fault and unable to identify quickly. 5G communication technology is adopted, positive and zero sequence current detection method is proposed, and generalized regression neural network (GRNN) is combined to realize real-time transmission and rapid decision-making of fault diagnosis in distribution network. The results show that this method can improve the recognition rate of ungrounded fault by more than 20%, and solve the problems of unreliable communication and low intelligent fault diagnosis.