The invention provides a vehicle built-in permanent magnet synchronous motor controlling method. The method comprises steps of 1, establishing permanent magnet synchronous motor mathematic models including a voltage equation model, an electromagnetic torque equation model and a torque balance equation model; 2, designing a sliding mode surface and a sliding mode control law, so as to achieve sliding mode control of the electromagnetic torque of a motor; 3, based on the electromagnetic torque value Te, performing decomposition to obtain a quadrature-axis current iq and a direct-axis current id; 4, based on iq, id, Udc, quadrature-direct axis voltage references U'q and U'd, obtaining quadrature-direct axis current reference values i<*>[q] and i<*>[d] by decomposition; 5, decomposing i<*>[q] and i<*>[d] to obtain the quadrature-direct axis voltage references U'q and U'd; and 6, based on the U'q and U'd, obtaining two phase stationary voltages U[alpha] and U[beta] by coordinate conversion, taking the U[alpha] and U[beta] as the input, and obtaining three phase reference voltages Ua, Ub and Uc after modulating the models to drive an inverter and the motor to work. The control method can ensure stable operation of the motor under any working condition.