Soil moisture is the main limiting factor for vegetation restoration and ecological construction in semi-arid loess hilly region. It is clear that the change of soil moisture with vegetation succession is an important basis for elucidating the interaction mechanism between vegetation and water in semi-arid ecosystem. This paper takes the Medicago sativa grassland abandonment process in the small watershed of the semi-arid loess plateau as the research object, through the dynamic monitoring of 0-1.8 m soil moisture in the four grassland communities of Medicago sativa community, Medicago sativa+Leymus chinensis community, Leymus chinensis community and Stipa bungeana community during the growing season of 2016-2018 and the measurement of soil moisture at a depth of 0-5 m were carried out to analyze the dynamic characteristics of soil moisture in different succession stages, and to explore the response of soil moisture to the process of Medicago sativa grassland reclamation. The results showed that: (1) In the process of Medicago sativa grassland succession, the soil moisture increased first and then decreased with the extension of community recovery time. The interannual dynamics of the second precipitation significantly affected the soil moisture response of different succession communities; (2) 0-0.4 m soil moisture is mainly affected by precipitation, so that there is no significant difference in the grassland communities at this level (P>0.05), while soil moisture content below 1 m is mainly affected by vegetation type, with significant difference among grassland communities (P<0.05); (3) with the succession of community, the soil moisture in the deep layer of 0-5 m increased gradually with the soil moisture content below 1 m, indicating that the soil moisture was recovered to a certain extent during the process of abandonment. The results reveal the change rule of soil moisture in the process of Medicago sativa grass fattening, which can provide theoretical basis for vegetation restoration and ecological construction on the loess plateau.