Normal>The stress-strain relation and shear strength characteristics of loess, which is taken from west area of Liaoning Province, are tested by trixial compression instrument in laboratory. The influence of water content to constitutive relation and shear strength of loess is tested and analyzed by means of remodeled samples with a series of different water content. The results show that: 1) the stress-strain relation is softening type under unconsolidated-undrained condition, which exhibits a way of brittle failure. It is changed from strain-softening into strain-hardening with increasing of water content in consolidated-undrained shearing condition. And in the condition of drained shearing test, the stress-strain relation is strain-softening in a low water content, it will be strain-hardening and slightly strain-hardening with increase of water content; 2) the shearing strength of samples will obviously decrease after saturated, namely, normal">c_UU is between 13.7 kPa and 363.3 kPa and normal">φ_UU is between 18.6° and 40.2°,but normal">c_CU can be changed from 0.2 kPa to 29.6 kPa, and normal">φ_CU is from 4° to 23.4°; and 3) there is a nonlinear decreasing relationship of shear strength indexes to water content. The cohesion and the internal frictional angle are changed in a semi-logarithm and a power function with water content, respectively. Consequently, a mathematical model to describe the constitutive relation of loess and a method to determine the index of shearing strength is suggested.