It has great important application value to study the relations between suction and moisture of unsaturated soil for its deformation and intensity. With the unsaturated triaxial equipment for expansive soil test

we analyze systematicially the multi-factors such as the components of mineral

the structure of hole

the stress state of soil and the stress history etc.

which affect soil-water characteristic curve (SWCC). Especially the components of mineral and the structure of hole are primary influential factors. Based on the measurement of matric suction indoor and outdoor

we think over synthetically the effect of multi-factors to fit and compare SWCC

also we build the model of power function. And according to SWCC

the otherness is obvious in the curve of dry-damp circulation indoor and not obvious in the curve outdoor

which is similar to the welter curve indoor. The permeability and shear strength etc. of unsaturated expansive soil can be calculated by combining the curve outdoor with welter curve

which has great superiority in solving problems of geotechnical mechanics.