Aiming at the problem of large overshoot of the traditional second-order self-imposed disturbance control in the speed control system of permanent magnet synchronous motor, an improved second-order self-imposed disturbance control method is proposed. Firstly, considering that the dilated state observer is slow in estimating the perturbation, a new fixed-time dilated state observer is designed. Secondly, in the state error feedback law, the hyperbolic sine function is used to design a new nonlinear function that is continuously derivable at the origin and segmentation points, thus solving the problem of the traditional nonlinear function that generates abrupt changes under certain conditions, and finally, an improved crayfish optimisation algorithm is proposed to rectify its parameters. Through Matlab/Simulink simulation and experimental verification on a semi-physical platform, the proposed control method not only effectively solves the overshooting problem, but also further improves the robustness and immunity of the system compared with the traditional self-immunity control.