According to the development status and characteristics of domestic spring machine at present， the computer numberical control （CNC） system for spring machine based on Computer Programmable Automation Controller （CPAC） is designed. The hardware composition of the CNC spring machine and the modular design and implement of control system software were mainly elaborated. The open and modularized spring machine CNC system were developed based on human machine interface (HMI) for human-computer interface,the general integration motion controller GUC series from Googol as the control core and the programming language of ST and the ladder diagram (LD). This design can meet the needs of modern spring production and improve the production efficiency.