This paper introduces the method for analyzing settlement data of tunnel in soft soil. The method is applied to the settlement monitoring analysis of some tunnels across the river. In the case study, the longterm monitoring data for shield tunnel settlement is discussed concretely. Firstly, unitary longitude settlement curves are gained, and the corresponding longitudinal curvature is calculated to investigate the rules of absolute settlement and uneven settlement varying from time. Secondly, based on the uneven settlement magnitude, the mechanical properties of shield tunnel are discussed by means of the equivalent axis stiffness continuous model of shield tunnel. In this way, the relationships between longitudinal curvature and crack of shield tunnel segment joint, the stress of tunnel concrete segment, and the stress of bolts for segment joint are found generally. So the crack and leakage of shield tunnel can be inferred consequently. Finally, the results gotten from analytical solution are compared with the field inspection information, and the favorable agreement is shown. Analysis of effect of long-term settlement on longitudinal mechanical performance of tunnel in soft soil offers guidance to evaluate the safety and serviceability, structural protection and waterproof design of shield tunnel in soft soil.