In order to meet the real-time performance of the full software CNC system, the full software CNC based on RTLinux is designed. Linux+RTLinux system is used as development platform, the timer parameter is changed by the method of hardware interrupt, and the real-time requirement of the CNC system is solved. The idea of modular design is used on CNC system to divide the function module, and the software design of the full software CNC system based on RTLinux is completed. C language is used as the main development language, the development of functional modules of the system management layer and the control layer is realized. Linear, circular interpolation function of CNC system can be realized.