Abstract: This paper analyzes the geological background and the process induced by the hydrodynamics of developing soil-caves in Wuxuan, a city in Guangxi Provence, china. Under ideal conditions, the mechanism model of the seepage failure of soil to forming soil-caves is the pipe flow. From the theory of the pipe flow, it establishes the expression of the hydrodynamics causing the soil-caves. Next, through the experiment designed to simulate the pipe flow, it obtains the critical shear stress 21.20 Pa to lead to soil-caves in the study area. The equivalent diameter of soil pores is 31.6 nm tested by the electron scanning microscopy. With the known parameters, it calculates the critical velocity of ground water 0.530 cm/min. Comparing the monitoring data of the ground water in the field with the critical hydraulic values, the study assesses the probability of the soil-caves collapse. The result shows that the current hydraulic condition doesn’t have enough the dynamic to form the soil-caves collapse in Wuxuan.