Based on the essential relation between a 3/12-phase double-winding AC-DC generator and an ordinary 3-phase synchronous generator, according to the method of analyzing the electromagnetic torque of a 3-phase synchronous generator under sudden short circuit, the electromagnetic torque of the 3-phase AC winding loaded double-winding AC-DC generator under DC side sudden short circuit is studied. The concise analytical expressions for alternating, unidirectional and total electromagnetic torques are obtained, which are verified by experiments. These expressions are concise and precise and have clear physical meaning, so they are especially suitable for engineering applications.