Abstract: In light of the situation where the deducted tunnel longitudinal stiffness effective rate (0.14~0.23) was smaller than the adopted value (about 0.7) of a shield tunnel in Shanghai, the traditional longitudinal equivalent continuous model was improved, and a new longitudinal equivalent continuous model was established that corrects the calculation formula for the eqnivalent bending rigidity based on the parameter equation for the ellipse and the consideration of the effect of lateral rigidity and influential scope of the annular joints, furthermore the constraint coefficent of soils and influence coefficent of segment eretion types were taken into account in the formula. Taking a specific tunnel in Shanghai as an example, the influence of lateral rigidity and the influential scope coefficient of the annular joint on the equivalent bending-resistant stiffness was analyzed. The calculation results show that assuming that“ellipse deformation”occurs in the tunnel, the effective rate of the longitudinal equivalent stiffness increases by 26%~50% compared with that by another models. The data were close to the actual application values and the rationality of the ellipse assumption was verified.