By taking the loess from Yangling area in Shaanxi province to prepare specimens, a series of direct shear tests are conducted to explore the deterioration characteristics of disturbed loess with different initial water contents and repeated freezing-thawing cycles. The experimental results indicate that when the water content is constant, the cohesion and shear strength both decrease to the minimum in three to five freezing-thawing cycles and reach an invariable value ultimately, and the internal friction angle of loess keeps constant basically. A tight relation between the shear strength and freezing-thawing cycles of loess can be seen. The negative effect of decrease in water content on shear strength is modified by interpolation, and a deterioration model of loess' shear strength is suggested. The relation between shear strength of loess and freezing-thawing cycles can be well described by the model, and a new effective method of confirming the deterioration of engineering mechanical properties of loess after repeated freezing-thawing is put foreword.