A reinforced earth retaining wall of a fill slope subgrade in Qinling-Bashan Mountains collapsed six years after its completion, resulting in the destruction of the road fence at the top of the slope and the damage of the houses at the foot of the slope. The failure characteristics of the reinforced earth retaining wall were found out through field investigations, and the inducing factors and formation process of the failure of the reinforced earth retaining wall were comprehensively analyzed combined with numerical simulations. The results show that the main failure characteristics of the reinforced earth retaining wall are the face slab collapses in a large area, and the reinforced filler behind the slab still maintains a good overall stability. The collapse of the reinforced earth retaining wall panel is mainly due to the fact that the fill slope blocks the original drainage channel, and the "anti-slide pile + retaining plate + reinforced earth retaining wall panel" in the retaining structure forms a relatively impermeable boundary, while the water infiltrated from continuous rainfall and domestic water cannot be drainaged in time, resulting in the rise of the groundwater level and of hydrostatic pressure. The failure process of the reinforced earth retaining wall is as follows:increasement of hydrostatic pressure, failure of bottom panel tie bar connection, increasement of upper and middle panel stress and overall failure of panel.