Abstract: Introduction During the double bus operation in substation, the conduction status of main and auxiliary switch contact are inconsistent, due to the main contact arc and the inconsistency of main and auxiliary contact stroke, which is named switch position abnormity. The bus protection can not judge the operation mode of bus bar and make incorrect action finally. Method In this paper, four kinds of position abnormity of switch and its influence to bus protection were summaried. Result The results show that a new auxiliary contact which is consistent to the arc status of main contact is putted forward preliminary. Conclusion This work provides some guidance for improving the selectivity of bus protection.