In order to improve the position estimation performance at high speed, this paper proposes a discrete-time observer for interior permanent magnet synchronous motor sensorless drives based on the state-transition discretization method. First, the common-adopted sensorless continuous-time domain modelling method is introduced and the corresponding drawback is analyzed. In order to overcome this drawback, a discrete-time model based on the state transition matrix is proposed considering the delay and latch eff ect of the zero-order-hold, and in this way the digital-controlled voltage command input and the discrete-time domain estimated back electromotive force can be considered in the state-transition equation in the same time. And then the closed-form sensorless scheme based on the proposed discrete-time model is introduced. Finally, the proposed sensorless scheme has been verifi ed by steady-state and dynamic experiments. The results show that the position error is deceased by 0.5°, and the system stability has been also greatly improved especially at high speed with a smaller position and speed error fl uctuation.