Abstract: To explore the possibility of guiding water-saving irrigation technique in paddy field based on the thickness of unsaturated soil layer, it is necessary to study the relationship between soil moisture content and the thickness of unsaturated soil. In this study, a pot experiment was carried out continuously for different water consumption intensities, and the quantitative relationship between soil moisture content and unsaturated soil thickness was established based on the real- time observation data of soil moisture content and the thickness of unsaturated soil. The results showed that: the thickness of unsaturated soil layer increased quicker as the water consumption intensity got larger and it took less time to reach the maximum. The soil moisture content decreased with time and was negatively correlated to the thickness of unsaturated soil layer. Then, a quadratic parabola relationship between soil moisture content and the thickness of unsaturated soil layer was established and showed that it was practical and feasible to use the thickness of unsaturated soil layer as the water control index to guide the irrigation. Finally, the relationship between soil moisture content and the thickness of soil unsaturated layer was applied to the practice of water-saving irrigation, and the minimum thickness of soil unsaturated layer corresponding to the minimum water content of guiding irrigation was found in different stages of rice growth under different consumption intensities in paddy field. The study could provide certain reference for water-saving management in paddy field in Heilongjiang, and a basis of the future calibration and simulation of the soil moisture content and water consumption in soil by using water movement model.