With regard to the problem that the traditional methods are difficult to precisely detect the demagnetization of permanent magnet synchronous motor (PMSM), an adaptive nonsingular terminalslidingmode control algorithm is discussed for PMSM. Firstly, the mathematical model of PMSM is established according to permanent magnet demagnetization condition. Then, adaptive observer and nonsingular terminalslidingmode observer (NTSMO) is constructed for permanent magnet demagnetization detection and the adaptive estimation of stator resistance is given. The stability of the sliding mode observer is proved by the Lyapunov stability theory. Based on the equivalent control principle of sliding mode variable structure, equation for permanent magnet flux linkage is constructed. Finally, it is verified by simulation experiments that after changing the stator resistance parameter, the adaptive highorder sliding mode permanent flux observer can detect the flux parameters accurately.