This changeover switch is used in the main circuit of diesel locomotive DMU to change the current flow direction of excitation windings of traction motors, so that can change the running direction of locomotive. The conversion between the traction and brake can be fulfilled through changing the winding connection of traction motors. This changeover switch complies with the IEC77 “ Specification of electric traction devices”, TB/T1333 “ General technology conditions of electrical apparatus of locomotive” and GB/T1457 “ Technology conditions of positional changeover switch of locomotive”. This series of electrical apparatus mainly consists of main contact system, auxiliary contact system and cylinder transmission system, so that it is applicable for the DF4B, DF8B and DF12 diesel locomotives.