The present invention relates to a method used for calculating step voltage of a gas insulated substation. On the premise of accurately calculating a shell circulation situation, a grounding situation and a shell potential distribution situation of a gas insulated substation, a three-dimensional electric field model under finite element analysis is established for soil situation and a grounding system in the substation, then potential distribution situation of the soil surface can be obtained, thereby obtaining a distribution situation of step voltage in the substation on this basis. According to the method of the present invention, the calculating precision is greatly improved, more accurate calculation can be performed for the problems in the substation, and effective prevention and maintenance also can be targetedly performed for the problems in the substation in the case of failure. The method also has certain economical efficiency, and can reduce unnecessary economic losses on the premise of targeted prevention.