In this paper, a robust speed control system with a permanent magnetic synchronous motor(PMSM) using a Kalman filter load torque observer is presented. Compared to other modern complex control algorithms, the observer algorithm is very simple and effective in reducing the effect of the disturbances. An IP speed controller using ITAE is used as the main controller, and the parameter controller (PC) is used to make the system robust with respect to rotor inertia negative variations; the PC is a parameter controller which selects a moment added. of inertia J according to the load torque to control the system response. Also, to overcome practical difficulties in obtaining inertia variation for the experiments, an electrical equivalent circuit was proposed and used. Finally a microcomputer-based system is implemented. Then simulation and experimental results are described to verify the effectiveness of the proposed algorithm.