Abstract: To study the reduction mechanism of earth pressure on retaining wall for light weight soil, the model tests on a large-scale rigid retaining wall are conducted. The uniform loads are applied on the filling surface by heavy stacking. When the remolded loess and light weight soil are used as backfilling behind the wall, the distribution laws of earth pressure at rest are analyzed respectively. The results show that the earth pressure at rest of the light weight soil gradually increases with the increase of curing period, but the increase range gradually decreases. The earth pressures at rest of the remolded loess and the light weight soil increase approximately linearly with the increase of filling depth. Moreover, they gradually increase with the increase of the upper loads, and the increase range of earth pressure at rest for the remolded loess is obviously larger than that of the light weight soil. By comparing their earth pressures at rest, it is found that the light weight soil has an obvious pressure reduction effect, and the greater the uniform loads applied on the filling surface, the better the pressure reduction effects of the light weight soil. The coefficient of earth pressures at rest of the remolded loess and light weight soil is not constant. The range of coefficient of earth pressure at rest for the remolded loess is 0.34~0.78, and that of the light weight soil is 0.22~0.55. When the uniform loads are applied on the surface of the filling, the traditional earth pressure theory has a high applicability to calculate the earth pressure at rest of the remolded loess, but the calculation error of the light weight soil is larger. Based on the model tests and traditional earth pressure theory, a modified formula for the earth pressure at rest for the light weight soil is proposed. It is found that the relative error is mainly 1.01%~23.13%. The characteristics of earth pressure at rest of the light weight soil are revealed through the model tests and theoretical calculation, which is of great significance to improving the earth pressure theory of the light weight soil.