为描述非饱和土的应力-应变特性，基于非饱和土三轴剪切试验，提出泊松比变化率（即切线泊松比随轴向应变的变化速率）的概念，发现非饱和土的切线模量和泊松比变化率均随轴向应变的增加呈指数衰减规律，基于此提出了一种描述非饱和土应力-应变关系的新非线性模型。该模型不仅能描述应变硬化，而且能描述应变软化；能对非饱和土三轴不固结不排水剪、固结排水剪、固结不排水剪试验的应力-应变关系进行描述；模型共包含6个参数，物理意义明确，确定方法简便。利用提出的模型对国内外文献中的三轴试验进行了模拟，结果表明，模拟结果与试验数据有很好的吻合度，从而验证了模型对试验数据的合理性和适用性。

In order to describe the stress-strain characteristics of unsaturated soils, based on the triaxial shear tests of unsaturated soils, a concept of change rate of Poisson’s ratio (that is the change rate of tangent Poisson’s ratio with the axial strain) is proposed. It is found that the tangent modulus and Poisson’s ratio rate of unsaturated soils under triaxial shearing attenuate exponentially with axial strain. Based on this law, a new nonlinear model for describing the stress-strain relationship of unsaturated soils is proposed. It can depict both the strain-hardening and strain-softening behaviors of unsaturated soils, and also it is suited to describe the stress-strain characteristics of unsaturated soils under unconsolidated undrained, consolidated drained and consolidated undrained triaxial shearing conditions. This model contains six parameters. All of these parameters have clear physical meanings, and their values can be determined easily. The triaxial shear tests in the open literature are simulated by using the new model, it is found that this model gives a satisfactory prediction of stress and strain of unsaturated soils compared with test data, thus the rationality and applicability of the proposed model are validated.