To elucidate the influence of prestress-related parameters of precast segmental box girder bridges on the stress distribution across the cross-section and longitudinal profile during the cantilever assembly and closure stages, a three-span prefabricated segmental box girder bridge was selected. Numerical simulations were conducted to investigate the effects of various prestress parameters during the cantilever assembly and closure stages on the structural responses and deformation characteristics of the bridge. The research findings indicate that the optimal tensioning control stress for the top slab tendons of precast segmental box-girder bridges is 0.70-0.75 times of the standard tensile strength value of prestressing tendons, concurrently necessitating the constraint that the cross-sectional area of the prestressing tendons should not fall below 0.000 98 m2(7?15.2 mm). The distance between the resultant prestressing force line of the single-side steel strand group in the top slab and its centroidal axis, namely, the eccentricity of the resultant prestressing force in the top slab, is recommended to be selected within the range of 0.22 to 0.26 times the width of the box girder. During the closure phase, the utilization of continuous steel tendons for both the bottom slab and the web was pretensioned, followed by the subsequent tensioning of localized tendons for midspan and edge spans, which facilitates a smoother distribution of alignment and cross-sectional stresses across various tensioning stages by promoting enhanced structural safety control throughout the construction period.