This text introduced the basic structure of the modern the servocontrol of d.c., the analysis designed the power convert telephone, control circuit, drive circuit, protection telephone and assistance the power supply etc. the each constituting the fraction.The article introduced the d.c. PWM servo drives device control principle and characteristicses, PWM system engineering inside relevant problem, and system stat, dynamic performance design computing.The method of design that adoption H type duotriode pattern, schema PWM control the transform telephone, used the big power in etc. in tube in switch in GTR a device in power transform telephone, use the waveform occurrence machine in control circuit, the vein breadth makes machine etc. the control the chip, adopting the voltage type PWM and current type the PWM the control the pattern, schema, composing site, voltage, current, three shut the ring feedback control the system.