Objective: The Shenzhen-Zhongshan Link, an expressway that connects the cities of Shenzhen and Zhongshan, has a total length of 6 845 m, of which the immersed tube section is 5 035 m long and uses a steel shell-concrete structure. The design and construction of the final joint posed notable challenges, provided the complex sea conditions and site-selection constraints in the construction area. As a solution, the Shenzhen-Zhongshan Link innovatively adopted the "prefabricated push-type construction method" for the construction of the final joint, considerably increasing the construction efficiency. This paper conducts a detailed mechanical analysis of the procedures involved in the "prefabricated push-type construction method" employed in the Shenzhen-Zhongshan Link. Methods: First, the detailed construction process of the underwater push-out final joint in the link is discribed. The underwater construction of the final joint in the link is split into six main processes, covering key construction steps such as steel-shell transportation, water pumping and pressure fitting, and steel tie rod welding. Subsequently, this paper conducts a model verification of the final joint during the construction phase. Monolithic finite element models are established for the push-out part and expanded part, and finite element calculations are conducted on the basis of the loads of each working condition to confirm structural safety. Finally, a detailed mechanical analysis of the underwater push-out process is conducted; this paper observes that the process involves changes in the internal forces of the steel rods and the deformation of the GINA waterstop. This paper observes potential structural safety risks in the relevant process. Therefore, theoretical calculations and finite element model verifications are conducted for this special stress condition. A theoretical analysis model is established, and the effect of rail friction on the rebound amount of the GINA waterstop is studied via formula derivation. A refined finite element model is established to analyze changes in the internal forces of the steel rods during the underwater push-out process. Results: The results of the model verification during the construction phase indicated that under all working conditions, the maximum stress and floor deformation of the push-out part and expanded part were within the design safety range. This suggested that the structural design of the "prefabricated push-type construction method" is relatively reliable with a considerable safety margin. The results of the mechanical analysis of the underwater push-out process showed that rail friction caused greater rebound on the upper side than on the lower side, hence generating greater tensile forces in the upper steel rods. Furthermore, the underwater push-out process may lead to uneven spatial distribution of internal forces in the steel tie rods. Conclusions: The "prefabricated push-type construction method" adopted for the final joint in the Shenzhen-Zhongshan Link exhibits relatively structural-stress characteristics during the construction phase. This paper verifies the most unfavorable conditions in each construction process, and the results show that the relevant structural design is reasonable with a sufficient safety margin. During the underwater push-out process, uneven spatial forces can be generated in the rods because of the influence of rail friction and the spatial distribution of the steel tie rods on the cross section. This study suggests that similar construction processes should monitor tie rod stress data and flexibly employ anti-backward devices to ensure structural safety.