In order to explore the influence of side filling load of upper-buried culvert on the foundation bearing capacity, based on the ultimate bearing capacity theory of Prandtl- Reissner and Terzaghi, studying the variation law and curve characteristics of silty clay, clay and sand foundation bearing capacity under the depth and width effects of culvert foundation. Based on the actual stress condition of culvert foundation, proposing the calculation diagram and improved calculation method of culvert foundation bearing capacity. The results of the improved calculation method are compared with those of the numerical simulation and the Terzaghi method. The results show that: (1) The depth effect and width effect of culvert foundation can improve the bearing capacity of high fill culvert foundation obviously. With the increase of foundation burial depth coefficient, the bearing capacity of silty clay, clay and sandy soil increases.(2) When the foundation width coefficient K is larger than 5, the increase rate of foundation bearing capacity of clay and sand decreases, and the increase rate of foundation bearing capacity of silty clay is larger.(3) The foundation bearing capacity of the improved method is 5.28% larger than that of the finite element method and 15.29% smaller than that of the Terzaghi formula method. The improved method is closer to the true bearing capacity of culvert foundation than the Terzaghi method.