Abstract: The characteristics of collapse and seepage of loess are studied through in-situ pit flooding tests in Ledu County, Qinghai Province of China. The continuous observation during and after flooding of intact loess ground using the settlement and in-situ TDR water content measurement systems reveals the seepage pattern and its effect on the self-weight collapse of loess, particularly, the temporal-spatial distribution of seepage in intact loess foundation is well recorded. Based on TDR water measurement detectors, the seepage process and seepage pattern of water in intact loess foundation are precisely measured to obtain the velocity of dispersion and its changing both vertically and horizontally at different stages of flooding tests, and the relationship between velocity and distance of water dispersion is established. Further analysis reveals the relationship between water seepage and self-weight collapse of loess. Based on this observation, a method to evaluate the susceptibility of self-weight of loess is proposed by calculating the time difference between the seepage front and commencement of self-weight collapse of loess.