Abstract: In order to prevent trip and damage of 110 kV power supply line caused by thunder and meanwhile satisfy demand of production increase, reform and extension design of ring network of 110 kV substation of Liuzhuang Coal Mine was done, lightning protection measures of overhead distribution lines including overhead ground wire and zinc oxide arrester were adopted according to its actual situation. The reform and extension design of ring network make whole power lines form a ring network of power supply, namely, the ring network can ensure to supply any load by power supply loop when a power line happens trip or damage caused by thunder, so as to solve reliability problem of power supply lines.