Abstract:The mechanical reinforcement provided by roots is remarkable. However,because the root zones of most plants distribute generally within 1.5 m underground,failure planes of deep seated landslides typically pass well below the rooting zone. As an important discharge way,the transpiration can lower groundwater table of slope aquifer. Because transpiration takes place mainly in intermittent periods of rain events or in dry season,it can not substantially reduce peak groundwater levels in precipitation. Vegetation cover has minimal effect in deep landslide mitigation. Dry crack,animal passage way,expanding fractures,and structural pores related to vegetation cover,constitute a relatively stable macrospore system in upper slope mass,which improve markedly the recharge environment of groundwater and make slopes absorb all precipitation except interception by vegetation. The compound circulation model of ‘Infiltration-groundwater runoff-transpiration’ in vegetated slopes lead to the continued increase of groundwater runoff rate and the gradually dropoff of rock-mass composite quality. Biogeochemical processes,such as root breathing and litter degrading,release acidic substances like CO2 and organic acids and raise the acidity of soilmass and the erosiveness of the infiltrating rain. At the same time,the pre-event water giving place to the event water in vegetated slopes makes saturation index of water-rock exchange phases keep a low level and chemical water-rock interaction can continue. Therefore,the contribution of vegetation to the deep seated landslide preparation is notable.