For a long time，due to the relatively weak monitoring of soil moisture and the late start of soil moisture constant study, there is no unified standard for constant soil moisture measurement methods, and there are some differences in the measurement results. This paper systemtically expounded the soil moisture constant determination method, providing the the reference for standardizing the determination process of soil moisture constants, providing the technical support for soil physical property studying, soil moisture monitoring and evaluation, and providing the reliable decision basis to the government departments for drought relief and disaster reducing.