Modified routine method is widely used in the calculation of the internal force of shieldbored tunnels, and the calculation parameters are generally selected according to the experience. In the paper, the key calculation parameters of ground penetrating shieldbored tunnel in the modified routine method, i.e., the stiffness reduction ratio (η) and the moment release ratio (ξ), are analyzed on basis of shellspring model, considering the nonlinear relationship between the bending stiffness and axial bending moment of the segment joints. Conclusions drawn are as follows: 1) For shieldbored tunnel with supershallow overburden, the minimum value in the specified range of specifications should be adopted for stiffness reduction ratio (η) and the maximum value should be adopted for the moment release ratio (ξ); 2) When the top of the tunnel is above the ground surface, value 1 should be adopted conservatively.