Over-deflection of beam in continuous rigid frame bridge has become an serious problem in recent years. The reason is complex. Some reseachers think that the bad quality of sectional joints in cantilever construction will cause additional shearing deformation and affect the beam deflection, this idea need to be further studied. In the paper, two three-dimensional models are built up based on a factual bridge, the simulation method of joints is studied, the influence of shearing deformation caused by sectional joints on beam deflection in construction is analysed. The study shows that shearing deformation of sectional joints has influence on deflection in cantilever construction, and it shouldn’t be ignored. This may be important to improve the loading property and renovate the design concept of this kind of bridge.