Abstract: The low-level radio frequency control system(LLRF) is mainly used to control the electric field and resonate frequency of the accelerating cavity to ensure the stable operation of the accelerator and output high-quality beam. The LLRF software provides a graphical user interface, and realize the functions such as data display and storage, as well as some algorithm like automatic logic and so on. A well-designed LLRF software improves the operability of the LLRF and reduces the amount of manual work and failure rate. This paper introduces the development and design of LLRF software for China spallation neutron source(CSNS) linac, mainly including feedforward automatic calculation, automatic frequency control of acceleration cavity, frequency detuning algorithm, automatic RF power up and so on. Finally, the amplitude and phase stability index of the system is better than the required design index, and meets the requirements of long-term stable operation.