The integration of distributed power sources into the distribution network will have an impact on the operation mode of the power grid, and even cause relay protection misoperation in serious cases. Based on the failure of two substations caused by the reverse transmission of a distributed power source, this paper analyzes the reason of the relay protection action, and puts forward the improvement measures from the management and technical perspectives; Based on 5G wireless communication technology, an active defensive distributed power supply access scheme is proposed; Using this scheme, a control device is developed and verified in the substation. The operation results show that the scheme can effectively complete the safety and control of the grid connection of distributed power supply, and improve the efficiency of operation and maintenance.