In order to follow up and apply this research work in practical engineering, this paper continues to study the structural strength deterioration test of undisturbed loess by moistening and freezing-thawing, and tries to establish the deterioration model of structural strength. The research results are as follows: Firstly, according to the compression curve of undisturbed loess, the concepts of structural strength, residual structural strength and structural strength damage variable are defined. And the damage variable can characterizing the process of strength degradation of loess structure is explained in detail. Secondly, based on Weibull distribution and damage mechanics strain equivalence hypothesis, the loess statistical damages models of sampling and sampling disturbance, moistening, and moistening and freezing-thawing cycles coupling action, statistical damage evolution function and basic equation of loess structural strength damage are established with volumetric expansion rate as the investigate variable. Finally, on the basis of the test data, the model parameters are determined, and the models are verified by taking a foundation pit loess in northern suburbs of Xi"an, and are in good agreement with the test. Research results can guide for on-site engineering design and construction.