The principle and structure of self-adaptive scaling factor fuzzy controller is introduced, which is composed of host fuzzy controller and auxiliary fuzzy controller. Auxiliary fuzzy controller produces a quantity to update real-time scaling factor according to control process error, variation of error and the relationship of error, to obtain better system control performance. According to characteristics of NC feeding servo system, the fuzzy controller is applied to control the NC feeding servo system. In order to check the dynamic performance and stable error of system, the controller is simulated with fuzzy toolbox and Simulink environment in Matlab. The results show that the self-adaptive scaling factor fuzzy controller is good for NC feeding servo system.