Taking the intact loess in a certain area in Xining as the research object, they were designed the three direction's slow freezing test under the closed system, the constant temperature and humidity thawing test and the triaxial shear test. Based on the Mohr-Coulomb strength theory of soil, the cohesion and internal friction were solved by using the shear strength envelope, and the variation of shear strength indexes under different freezing thawing temperature gradients are studied.The results show that:with increase of temperature gradients, the cohesion decay rate is remarkable, and it is -15~15℃ for the most disadvantageous freeze-thaw temperature gradient when the cohesion is minimum;The cohesion of frozen-thawed loess is related to the cold end temperature and thawing temperature;Compared with cold end temperature, the thawing temperature is the dominant factor when the moisture content is lower and the temperature at the cold end is lower, or the temperature at the cold end is higher. With the increase of the cold end temperature, the cohesion of samples with different moisture contents decrease firstly and then increase, the most disadvantageous moisture content is 18.34%.The internal friction shows irregular fluctuations, and the extent of variation is about 0°~14°. The calculation formula of the cohesion with the cold end temperature and moisture content is fitted by the experimental data. The experimental formula can better describe the variation characteristics of cohesion.