Abstract: Taking the Chongqing Xinsen Avenue cut-and-cover large-span prefabricated assembled tunnel project as the research background, a new type of assembled tunnel structure based on composite joints is proposed. A strata-structure numerical model is established, considering the influence of contact relationship, backfill hardening process, and compaction construction process. The mechanical behavior of a three-piece composite joint structure at the vault, a two-piece cast-in-place structure at the vault, and a traditional integral cast-in-place structure during the whole backfilling construction process is simulated and analyzed. The accuracy of the model is verified through comparison with field measurement data. The results show that during the backfilling stage, the composite joint structure exhibits superior deformation control capability, and the distribution of axial force and bending moment is more uniform. Compared with the two-piece structure and the integral cast-in-place structure, the vault settlement of the composite joint structure is reduced by 33% and 46%, respectively, and the peak bending moment is reduced by 82% and 40%, respectively. By optimizing stress distribution and enhancing overall stiffness, the composite joint effectively improves structural safety.