We model the rotation process of the motor for variable-order fractional control, which has been active in recent research, and perform numerical simulation of its optimal control and automatic control process. In this paper, we verify numerical method and error estimation of variable order fractional linear dynamic system with time-varying coefficients, a variable-order fractional PID controller design method where the integral of the absolute error with time weight is minimized is proposed using particle swarm optimization algorithm and demonstrate its effectiveness through numerical simulation for DC motor speed control. Numerical experiments show that the performance of the VFPID controller is superior to PID and FPID, especially VFPIDB (B-type variable order FPID) controller has the best performance. Finally, when the differential order varies, the subtypes of variable-order fractional derivatives are analyzed for the effects on the control objective, its effectiveness is newly clarified, and their research and practice is highlighted.