Abstract: In order to explore the soil moisture migration mechanism and its ecological effect in the cold and arid open-pit coal mining area, a long-term in-situ test was carried out to observe the soil moisture, taking the open-pit coal mine in eastern Mongolia grassland area as the study area. The results show that: The shallow soil moisture content is mainly affected by rainfall in non-freezing period, while the soil moisture content is significantly affected by soil temperature in freezing period. Besides, the saturated permeability coefficient of soil in depth less than 50 cm is greater than 150 cm/d, but that of soil in depth greater than 50 cm is only about 20 cm/d, which indicates that the saturated permeability coefficient of soil decreases with the increase of soil depth, and then the soil moisture formed by rainfall infiltration mainly remains in the root action layer within 50 cm depth. The groundwater depth in the study aera (>10 m) is much greater than the critical depth of groundwater recharging to the vegetation (3.52 m). Meanwhile, the vegetation index is positively correlated with the annual rainfall, which indicates that the soil moisture is the most important water source for maintaining the water consumption of vegetation in the region. Moreover, the soil moisture content in freezing-thawing period is recoverable or even higher than that in the non-freezing-thawing period, and the vegetation root zone presents a good soil moisture holding capacity due to the special soil layer structure. Both of the two factors are of positive significance for vegetation growth. The research results could provide reference for the ecological environment protection and restoration in cold and arid open-pit coal mining area.