To investigate the influence of the culvert side filling load on the bearing capacity of the foundation for separated foundation culverts and to establish a method for calculating this bearing capacity, the theoretical formula of foundation bearing capacity of separated foundation culvert considering culvert side filling load is derived by assuming sliding surface method. At the same time, the settlement and deformation characteristics of separated foundation culvert under different foundation soil and culvert side filling height are studied by finite element software. The results indicate that culvert side filling load enhances the foundation bearing capacity of the separated foundation culvert. The allowable bearing capacity of the foundation can be determined according to the post-construction settlement of 20 cm as the control index. It is economical, reasonable safe, and reliable to correct the foundation bearing capacity of a separated foundation culvert under the action of culvert side filling load by using the formula provided in clause 4.3.4 of the 'Highway Bridge and Culvert Foundation and Foundation Design Specification.