On the base of the determination of the soil - water characteristic curves and field moisture capacity of undisturbed soil samples of L_5 - S_8 in Luochuan,we analyzed the properties of moisture preserve,supply and storing and effective moisture content,and discussed preliminarily the different causes of soil - water characteristics of L_5 - S_8 . The results indicate that the soil - water characteristic curves of L_5 - 1 - S_8 - 2 are in well accordance with Van Genuchten model and the values of R~2 are all above 0. 98. The water - preserved properties of L_5 - 1 - S_8 - 2 become weaker with the increase of suction value in 0 ~ 85KPa. The water - preserved properties of the L_5 - 1 - L_8 - 2 are stonger than that of the S_5 - 1 - S_8 - 2,and the water - preserved properties of the L_5 - 1 - L_8 - 2 are weeker than that of the S_5 - 1 - S_8 - 2. The properties of water supply of L_5 - 1 - S_8 - 2 become weaker with the increase of suction value in 0 ~ 85KPa,and the properties of water supply of the L_5 - 1 - L_8 - 2 are stonger than that of the S_5 - 1 - S_8 - 2. The direct reason of properties differences of L_5 - S_8 is the different pore size distribution and clay content etc,and the underlying reason is the cold - dry and warm - wet climate change in soil development process.