From the viewpoint of the surrounding building's impact on calculated building's expanded width,the influence of the surrounding building on the equivalent area was analyzed under three cases:the surrounding buildings of the same height,higher or lower than the calculated building.Then it is concluded that the height,the relative location and surrounding degree of the surrounding building have a great influence on the equivalent area of a building,which can not be simply expressed by a constant location factor in the calculation of equivalent area considering the influence of the surrounding building.More precise calculations should be done according to the actual situation to improve the accuracy of the lightning risk assessment.