An artificial grounding fault test in 110 kV Dalü smart substation for the first time in China is carried out by Zhejiang electric power corporation. This artificial grounding fault test not only verified the reliability of non-conventional instrument transformer and intelligent relay protection system， but also tested electromagnetic compatibility（EMC） of secondary equipments in smart substation under the system fault. The EMC faced by smart substation is analyzed from three aspects: the variation of electromagnetic field of industrial frequency， electromagnetic interference of secondary circuit， and electromagnetic interference of communication circuit. The corresponding solution scheme is also proposed.