Most of the coal is used for thermal power generation in China, but a large number of fly ashes are produced after coal combustion. At present, the comprehensive utilization of fly ash is still insufficient, so it needs to find a new way of utilization. Meanwhile, large-scale underground coal mining leads to land collapse and ecological environment deterioration. The surface subsidence is the original source of mining damage, and that the efficient controlling subsidence method is backfilling in goaf with river sand, gangue and fly ash. In recent years, the backfilling technology has made great progress, and the backfilling position has developed from the traditional goaf to the internal overburden. In this method, the fly ash slurry is backfilled into the separation layer by ground drilling holes, which can actively control the surface subsidence and subsidence speed without affecting the normal coal production. Therefore, it has realized “Concurrent Mining and Reclamation” for protecting agricultural land. Finally, the surface dynamic subsidence calculation model is mentioned in this paper, which is suitable for this mining case. The results evaluate the effect of surface subsidence damage risk by fly ash.