This paper analyzes the application of static multicast technology in data sampling communication of intelligent substation, describes the phenomenon of abnormal data sampling caused by network storm or protection device caused by static multicast setting error, and states that improper multicast mechanism can cause the protection device to produce maloperation or rejection results. A power switch maintenance system based on static multicast search mode is introduced in view of the lack of detection means in intelligent substation power switch. The system dynamically sends multicast streams with different MAC addresses to one port of the switch, collects and counts the multicast streams of other ports of the switch, searches the MAC addresses of all ports of the switch by using a closed loop test method of one-port multi-port receiving, and forms a static multicast configuration table for each port of the power switch. Experimental results show that the method of multicast search in closed-loop mode can test the MAC address table of power switch, thus it has good practicability.