Considering the problems of internal and external disturbances in permanent magnet synchronous motor(PMSM) including modeling errors, sudden load variation, etc, which affect the stability of speed control, a load estimation-based composite active disturbance rejection controller(ADRC) for PMSM speed regulation is proposed. ADRC is adopted to replace the PI controller in the speed loop for improving the performance of control system and solving the contradiction between system rapidity and overshooting. A load torque observer is designed to solve the problem of slow response to sudden load variation from ESO by directly estimating and compensating the load torque in real time via speed and current signals. Based on Matlab/Simulink environment, a semi-physical experimental platform of composite ADRC for speed regulation is constructed, and compared and verified with traditional PI control and linear ADRC. Promising results illustrated that the proposed load estimation-based composite ADRC reduces the speed variation by more than 30% compared with conventional controller when load variation abruptly occur, and has superior ability of disturbance rejection and speed regulation performance.