Abstract: Based on the collaborative working mechanism of culvert-filling-foundation, the load reduction mechanism of a culvert with reinforcement is analyzed. Mechanical model of the culvert with reinforcement is established through theoretical analysis, and the expression of earth pressure acting on geogrid is derived theoretically. Considering the support effect of filling under the geogrid, the stress and deformation of goegrid are analyzed to derive deflection calculation formula of geogrid under load of filling, and then the pressure acting on the top of the culvert is calculated by force analysis. The calculated results by the presented method are in good agreement with those by finite element methods and the field test results recorded in literatures, especially when the fill is high. Finally, based on the presented method, parametric analyses are performed to study the main factors which affect the pressure on the culvert such as embankment height, modulus of loose fillings on the culvert and stiffness of geogrid.