In order to realize the personalized customization and real-time adjustment of the therapeutic parameters of the rehabilitation electrical stimulation system, a closed-loop electrical stimulation system for lower limb muscle strength rehabilitation based on modulated medium frequency electrical stimulation was proposed in this paper. A low-frequency modulation and medium-frequency stimulation circuit was designed, and a support vector machine regression prediction model between the electrical stimulation parameters and the Angle of the knee joint was established based on the genetic algorithm. A closed-loop feedback system based on fuzzy internal model control PID was built to achieve a more accurate and stable parameter setting effect. The knee motion experiment showed that the subjects were closer to the expected joint motion trajectory without pain. The maximum root mean square error between the knee motion Angle and the expected value in the 30 groups was 10.21°, and the minimum root mean square error was 5.48°. Compared with traditional low-frequency electrical stimulation, the mean amplitude of myoelectric stimulation was increased by more than 20 microvolts. The parameters of the electrical stimulation system proposed in this paper can be realized from person to person, and can be adjusted in real time according to the closed-loop feedback results. The system can effectively activate muscles and improve muscle strength, and has a good application prospect in the gait training of muscle strength rehabilitation.