Abstract: The BBM model of unsaturated soil is analysed, studied, validated. And a modification is further maked to the BBM model, so that the model is more consistent with the variation of matric suction in unsaturated loess. The iterative calculation method of BBM model in the literature is performed under the stress path of b-constant and σ3-constant with b=0. A revised on the existing calculation method, and then the calculation method of BBM model under the stress path of b-constant and p-constant with b=0 is given. Based on the results of the true triaxial suction experiments of unsaturated loess, the relevant model parameters of the BBM model are obtained, and the corresponding calculation method is used to predict the test results of the unsaturated loess under the stress path of b-constant and p-constant with b=0. In order to consider the nonlinear change of model parameters with matric suction for unsaturated loess, a hyperbolic function is adopted to modify the BBM model. The modified model is verified, and the results show that the overall prediction result of the revised model is ideal, especially the prediction result under low matric suction and low net mean stress is more ideal than the original model.