Abstract: Joint stiffness K θ is an important parameter for the design of circular prefabricated lining. Presently, there is no perfect theoretical way but test to determine the value of K θ.This paper proposes a joint mechanical model, which substitutes the joint bolts and liner layers with springs. The non linear equations describing the relations between the force applied on the joint and the strain caused by the force is given. To avoid extracting the non linear equations, a simplified K θ equation is derived. The rotatory angle, tension width and bolts tensile force can be calculated from the model. The correspondence between theoretical value and test value proves the validity of the model. The effect of various factors on the joint stiffness is also simulated by using the model, which shows reasonable results.