Abstract: This pater is to study how to control automatically the pellet fat spraying machine by the microcomputer system. According to the demands of design, a programme of the closed loop computer servo control system is determined with the electromagnetic adjustable speed motor and gear pump as the controlling objects and with the rate of spraying as the controlling parameters. The control target will be reached when the parameter is keeping on constant.The PID control algorithm is selected on the basis of the finding mathematical model of the objects and of the analysis on the characteristics of the model. The PID parameters are also adjusted and tested.Use the software of main block and other seventeen function blocks through the sensors, filter elements, amplifiers, A / D converter, D / A converter and other executive actuators of the system, All the working conditions and faults can automatically be detected and adjusted. The results can automatically be printed out and shown on screen, too. And it has the function of automatic warning and key-board control as well.Finally, the comprehensive evaluation of this control system is made.