In order to realize the fiveaxis linkage processing of CNC machine tools, the improved design method of the control system structure based on the domestic blue sky series CNC system was put forward. The NC system was divided into the task layer and the moving layer, and the fiveaxis transformation unit was integrated in the moving layer. Based on the classification of the fiveaxis machine tool and the analysis to its geometric information, the fiveaxis motion library of the machine tool was designed. The forward and backward motion transformations of CA swinging head were deduced. Based on the improved system and the fiveaxis motion library, the center control of the machine tool and the 3D radius compensation end mill were designed and analyzed. The improved system has good portability, which can directly execute the tool position and direction instructions in NC machining.