In the grassland mining area, the scarcity and barrenness of topsoil are the important factors restricting the ecological restoration. Biochar, as an effective means to improve the quality of soil and promote the growth of crops, has been widely confirmed, but there are few studies on the effects of the growth of vegetation on the reconstructed soil. In this study, we used topsoil (T), coal refuse (C), waste rock and soil (W), and fly ash (F) of Inner Mongolia grassland mining area to reconstruct five kinds of surface soil, and material ratio is T=1 (D1), T:C:W:F=2:1:6:1 (H3), T:C:W=2:2:1 (H10), T:C:W=3:3:4 (H11), and T:F=2:3 (H15), respectively. The effects of straw biochar at different pyrolysis temperatures (300 ℃, 400 ℃, and 500 ℃) and different application rates (0, 6, 12 and 24 g/pot, namely 0, 7.5, 15 and 30 t/hm²) on the growth of Medicago falcata were analyzed. The results showed that: 1) straw biochar had different degrees of inhibition on emergence of Medicago falcata in both original topsoil and the reconstructed soil, but showed positive excitation effects on plant height, leaf area and aboveground biomass. 2) For the reconstructed surface soil, the best treatment of biochar to promote the growth of Medicago falcata is D1\H3\H10-500-24 (30 t/hm²), H11-400-6 (7.5 t/hm²), and H15-500-12 (15 t/hm²), respectively. It is not that the higher the pyrolysis temperature and application rates of biochar, the better the effects of Medicago falcata improvement. 3) Under the same biochar treatment, straw biochar had different effects on the growth of Medicago falcata at seedling stage due to the heterogeneity of the physicochemical properties of the reconstructed surface soil. The emergence rate and aboveground biomass of Medicago falcata in the reconstructed soil could hardly exceed those in the original topsoil, while the plant height and leaf area of that could reach those in the original topsoil.