A full-speed Sensorless control algorithm for interior permanent magnet synchronous motor (IPMSM) is introduced in this paper. Pulsating high frequency (HF) injection is used in the low speed region and sliding-mode observer (SMO) is used in the high speed region. In the transition region, a new transition scheme combining pulsating HF injection and SMO is proposed. The transition region is divided into speed transition region and angle transition region. The speed transition region is set as half of the angle transition region. The system instability caused by the transition point is avoided when transition from the high speed region to the transition region. Pulsating high frequency injection and sliding-mode observer have their own phase-locked loop (PLL) parameters which can be easily regulated. The advantages of both methods can be preserved. Simulations are carried out and the results prove the effectiveness of the method.