Abstract: Malan loess was a special water sensitive geological deposit,whose physical,mechanical and hydraulic properties changed obviously under the softening action of water.Based on the investigation,in-situ and Lab tests on Malan loess carried out in Utrecht University of Netherlands and Lanzhou of Gansu Province with different methods,the water sensitivity,the hydraulic and shear strength properties of Malan loess were studied.The boundary of the brittle and plastic deformations was found,and some important critical indices of Malan loess were dexeloped.