Abstract: In calculating the lining stresses of a pressure tunnel with circular cross-section it is generally assumed that the rock mass is elastic. However, this assumption does not often accord with the characteristics of rock mass deformation. This paper presents a method of calculating the lining stresses, in whieh the test results of elasto-plastic deformations of rock mass are considered and it is treated as linear strain-hardening material. The critical interior water pressure ia the tunnel which creats the plastic deformations of rock mass is given. It is also indicates how to determine the parameters of rock mechanics.