Laying a flexible cushion or backfilling lightweight soil behind the retaining wall has important engineering significance for its optimized design and cost reduction. By carrying out model tests of retaining walls under different level of loads, the magnitude and distribution characteristics of the lateral earth pressure when laying EPS flexible cushion, backfilling lightweight soil and applying it simultaneously are analyzed, and the load-reducing effect is discussed. The result shows: when the retaining wall is paved with flexible cushion, backfilled with lightweight soil, or both applied, the lateral earth pressure exhibits a “bulging” nonlinear feature that increases first and then decreases with the burial depth, and the maximum value of earth pressure generally appears at half of the wall height; under the same loading, the load-reducing effect of backfilling lightweight soil is relatively weak, achieving a reduction rate of 10%-25%, the maximum load-reducing rate of laying a flexible cushion is increased by 1.5 times compared with lightweight soil, when both are applied, the load-reducing effect is the most significant, and the maximum load-reducing rate is increased by nearly 3 times; the load-reducing effect of the flexible cushion decreases with the variation of thickness, the foam content is more sensitive to the load-reducing rate of the backfill lightweight soil. In the engineering project, a medium-thickness cushion is an optimal choice, if the applied load of the backfill is large, the content of the backfill lightweight soil can be appropriately increased.