Abstract: When the mechanism of flow slide of loess landslides is discussed, it can find the residual strength plays a major role. The evaluation of residual strength requires a better understanding of undrained saturated loess behavior. Based on the loess landslide occurred at Gaolou village, Shanxi province, the stress state and the increasing model of pore pressure is discussed under stress-controlled undrained triaxial consolidation experiment. The parameter determining the behavior of loess is discussed. Steady state line of saturated loess is established. This line can be used to distinct whether flow slide will occur after liquefaction of loess. According to the test results,the mechanism of flow slide in Gaolou landslide is analysised.