Servo system is an important part of an Infrared Search and Track (IRST) system in a fighter plane, which includes scanning mechanisms, racemic mechanism, focusing mechanism, aperture adjuster, shaking-mirror modulator and system control software. This paper firstly describes the servo system of the IRST system, and then lays emphasis on design of control method. An intelligent controller is given and its parameters are defined. Finally the result is presented to demonstrate the effectiveness of this design.