The overburden of high embankment culvert is over 10 m, such high fill always leads large earth pressure on the slab of the culvert. The imperfect ditch covered with geogrid method was employed to reduce the vertical earth pressure on the slab. A series of numerical analyses were performed to investigate the load reduction effect of the imperfect ditch. In the simulation, the number of geogrid layers, the geometry of the load reduction ditches, as well as the location and the stiffness of the geogrid are investigated to analyse the influences on the vertical earth pressures. The results show that the slope angle and the height of the ditch, the plane stiffness of the geogrid have great effect on the load reduction efficiency, ditches with higher height and a slope of 90°lead to a significantly reduction on vertical earth pressures on the crown of culverts. The width of load reduction ditch, number of geogrid layers, the location and spacing of the geogrids have little effect on load reduction, the results can provide references for load reduction of slab culvert.