Abstract: Ground water states in the subgrade of mountain highways in river environment are often affected by the hydrological conditions of the river,so that the magnitude of active earth pressure acting on the retaining structure of the subgrade should be affected by many factors such as the seepage condition of the ground water and vehicle loads.Based on the basic assumptions of Coulomb’s theory,some simplifications on the structures of the subgrade and the retaining wall and related applicable codes of China,three solutions for computing the active earth pressures of three different cases,in which the retaining walls were provided with effective drainage systems along the soil-structure interface,effective drainage systems along the base of the backfill of the subgrade,and noneffective drainage systems,respectively,were suggested.Various influence factors on the coefficients of active earth pressures such as the effective internal friction angle and saturated unit weight of the backfill of the subgrade,the soil/wall friction angle and the vehicle loads were investigated.It was emphasized that in the design of the retaining structure of the subgrade,the effective drainage system placed along the base of the backfill of the subgrade was better than that placed along the soil-structure interface,and that in order to keep the stability of the retaining wall,the vehicles running on the mountain highways in river environment should be never allowed to be overloaded.