With the rapid development of urban construction, new structures inevitably induce the secondary loading on the top of existing high fill open-cut tunnel. In order to characterize the influence of the new secondary loading due to backfilling on vertical earth pressure on the top of high fill open-cut tunnel, the relationship between the geogrid deformation and the soil settlement is established by using the elastic theory of soil settlement, based on the formulation of earth pressure on the load reduction structure. Meanwhile, the effect of the secondary loading is considered. The method for calculating vertical earth pressure on the top of high fill open-cut tunnel before and after the load reduction is further improved. Numerical analysis models are established, and the numerical results are compared with the results obtained from the proposed procedure in this paper. The results show that the theoretical results are close to the numerical results, with the same regularity. The load reduction measure has a great impact on the backfill earth pressure on open-cut tunnel. The higher the fill, the more significant the effect of load reduction, and the smaller the practical earth pressure on the top of open cut tunnel. The calculation of vertical earth pressure on the top of open-cut tunnel under the secondary loading should consider the influence of soil settlement rather than a simple superposition.