In the aim of identifying the influencing factors and their effects on load reduction effect for culvert beneath high fill, the method and mechanism of load reduction by reinforcement bridge are introduced firstly. On this basis, by means of numerical simulation, the influences of number of geogrid layer, width, height and lateral slope angle of load reduction ditches, as well as properties of filling material on the vertical earth pressure and the load reduction effect are investigated. Results suggest that the modulus of the filling material in the load reduction ditch and the height of the ditch have great effect on the load reduction. Ditches of larger height and lower material modulus lead to significantly better load reduction effect and less vertical earth pressures on the crown of culverts. The width of load reduction ditch, number of geogrid layer and internal friction angle of backfill material have little effect on the load reduction, but the increase of the width of the load reduction ditch results in more uniform internal forces for the culvert and a decrease of bending moment.