The steady state strength (i.e., residual strength) plays a major role in the flow sliding mechanism of loess landslides. The evaluation of residual strength requires a better understanding of undrained saturated loess behavior. The steady strength of saturated loess is examined using stresscontrolled undrained consolidation triaxial test. Two typical stress-strain behaviors of saturated loess are steady state behavior and quasi-steady state. The majority situations exhibit steady state behavior. Only loose loess exhibits quasi-steady state behavior. According to the test results, steady state line and steady state strength line of saturated loess are established. These lines can be used to analyze the mechanism of flow slide. It can use the angle of internal friction and cohesion to describe the steady state behavior of saturated loess. The meaning of these parameters is discussed. The difference of irrigation-induced landslides of loess and seismically-induced landslides of loess is analyzed. If the landslides induced by earthquake, the steady state strength (residual strength) plays a major role. If the landslides induced by irrigation, the peak strength plays a major role.