Bridges with main spans ranging from 100 to 200 m are predominantly prestressed concrete continuous rigid-frame bridges. In engineering practice, such structures commonly suffer from girder cracking and non-convergent long-term mid-span deflection. Structural analyses employing two-dimensional frame models established via MIDAS are primarily based on elementary beam theory, yielding simplified stress and deformation results that fail to capture three-dimensional spatial effects such as uneven stress distribution in box girders and localized stress concentrations, thereby limiting the elucidation of long-term deflection mechanisms. In contrast, a three-dimensional solid finite element model established using ABAQUS can comprehensively account for influencing factors such as shear lag, warping, distortion, and localized stress concentration, thereby achieving higher analysis accuracy. To address these limitations, this study takes a prestressed concrete continuous rigid-frame bridge with a main span of 240 m as the research object. A three-dimensional solid finite element model is developed using ABAQUS, and a user subroutine for concrete shrinkage and creep is programmed using Fortran to enable long-term effect prediction and spatial stress evolution analysis. The objective is to provide a reference for structural design optimization and long-term deflection control. The results indicate that stresses in the top slab and web are concentrated at segment interfaces, closure segments, and the 0^# block; over time, the maximum stress at segment 0^# exhibits a decreasing trend as mid-span deflection increases. Within 20 years after bridge completion, the maximum stress in the web remains consistently higher than that in the top slab. The stress distribution near prestressing tendons exhibits fluctuations, with pronounced concentrations at casting segment interfaces, anchorage zones, and segment 0^#. The diaphragm of segment 0^# and its connections with the top and bottom slabs are identified as high-risk zones for potential cracking damage.