Reasons of lightening and conditions of grounding grid in 35kv transformer substation of Tunlan Mine were explored and analyzed, measures and keys of lightning protection for substation secondary system were proposed. Through setting separate low resistance corrosion resistance of grounding grid in secondary system, making strict separation for primary and secondary equipment grounding, as well as building three-level lightning for power supply of secondary equipment, frequent failures of 35kv secondary equipment due to lightning were improved. At the same time, this transformation of lightening protection was summarized and analyzed.