Abstract: Through analysing and comparing kinds of the intermediate principal stress forms under plane strain conditions and based on the particular conditions of stress-strain in oedometric experiments, an expression of the intermediate principal stress that is related with parameters of soil properties is deduced and confirmed. The expression is simply confirmed by parameters gained by triaxial compression experiments, and it can also simplly reflect the influence of soil mass stress history on soil strength. By combining SMP criterion and Lade criterion with the expression of the intermediate principal stress, the relationship of parameters of soil properties is established between plane strain state and triaxial compression state. Analysis and comparison of the experiment data show that the intermediate principal stress proposed herein well reflects the practical behavior of the soils mass and is very suitable for SMP criterion and Lade criterion.