The utility mode relates to a prevent back -emf alternating -current permanent -magnet electricity transmission system has solved the problem that there is the back -emf phenomenon in the synchronous traction motor trouble of current permanent magnetism. Including traction inverter, two high voltage isolator and two permanent magnetism traction motor, traction inverter includes battery charging unit, copped wave unit, filtering unit, the control unit and two inverter unit in advance, and two inverter unit's output corresponds with two high voltage isolator's one end and is connected, and two high voltage isolator's the other end corresponds with two permanent magnetism traction motor's input and is connected, high voltage isolator still is provided with auxiliary contact, and auxiliary contact and the control unit are connected. The utility model discloses real -time supervision switch developments play moreover and keep apart highly compressed effect, prevent the further expansion of trouble, can break off a high voltage isolator alone simultaneously, but the normal operating of another permanent magnetism traction motor, drive vehicle operation.