The reliability and volume of the propulsion motor are required strictly in underwater vehicles. The integrated motor propulsion (IMP) system adopts the sensorless control technology, which can reduce the volume of the electric propulsion system and improve the reliability of the system. In the vertical propulsion system, the dynamic response of the motor system is highly required. In order to improve speed response of the sensorless controlled permanent magnet synchronous motor, the dual dq coordinate switch strategy is adopted to integrate the IF start and the sliding mode observer (SMO). This scheme can improve the starting smoothness and shortens the starting time, which is validated by the comparative experiments.