Bus switching is a very frequent and complex operation, a slight mistake will bring about an unexpected incident. In this paper, during the operation process of "110kV east and west bus turn to the normal operating mode" in 220kV substation, on the top of B phase of X110 east disconnect, severe electric arc suddenly arises and it's treatment process is introduced. The reasons causing this phenomenon are find out and operation methods and considerations are put forward in bus Switching.