The surge of compressor and methods of anti surge are expatiated. The advantages and disadvantages are compared between these two methods. Considering the actual status of power plant, the anti surge method for gas compressor is raised. The models and functions of mostly important equipments are introduced simply. Based on this, the structure, control elements, calculation methods, open-loop and close-loop control functions of the anti surge system for gas compressor are educed. The calculation-al methods and response line shifting function in PROTRONIC 500 is explained in detail. The problem and amelioration of this system is explained simply.