Abstract: The BBM model for unsaturated soils is analyzed, studied and validated. A modification is further made to the BBM model, so that the model is more consistent with the variation of matric suction in unsaturated loess. The iterative calculation method for the BBM model in the literature is performed under the stress path of b-constant and σ₃-constant with b=0. A revision is made on the existing calculation method, and then the calculation method for the BBM model under the stress paths of b-constant and p-constant with b=0 is given. Based on the results of the true triaxial suction experiments on 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 paths 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 predicted results of the revised model are ideal, especially the predicted ones under low matric suction and low net mean stress are more ideal than those of the original model.