Abstract: In order to quantitatively evaluate the impact of open-pit mining on grassland ecosystems, taking Yimin Open-pit Coal Mine as an example, the vegetation net primary productivity (NPP) index was selected, to calculate the long-term series of NPP using 21 satellite remote sensing data from 1985 to 2018, then quantitatively evaluate the impact of open-pit mining on the surrounding grassland ecosystem and the ecological restoration effect of the waste dump. The results indicate that, the open-pit mining has resulted in a NPP loss of approximately 10% to 30%. As the recovery time increases, the vegetation of the waste dump continues to evolve towards natural vegetation, and NPP also increases and tends to stabilize. After stabilization, the NPP of the external waste dump has reached about 90% of the average annual NPP of the unaffected area, and vegetation productivity is close to the level of natural vegetation productivity. However, the average NPP of the inner waste dump and the northern outer waste dump with shorter recovery time only reaches about 50% of the annual average NPP of the unaffected area. The ecological reconstruction and restoration of open-pit mines is a long-term process, and it takes more than 20 years for the vegetation succession of the external dump to stabilize. It must be promoted synchronously with open-pit mining activities and persisted in the long term.