Abstract: Green mining is an important prerequisite for the sustainable development of coal mines under the goal of “carbon peak and carbon neutrality”. Grouting of overburden separated layer is an important technology for reducing damage to surface structures caused by coal mining and achieving green mining. In order to study the key technology of grouting of overburden separated layer in mines with “no-typical” key layers affected by faults, as well as the physical properties and applicability of the slurry, the 921103 coal mining face is taken as an example in this paper. By utilizing theoretical calculations and experiments, combined with on-site practices, the lithology of the overburden rock above the coal mining face is analyzed. Based on the mining geological conditions, it is determined that the upper rock strata of the face belong to the “no-typical” key strata type and multi-layer grouting technology should be adopted. This paper studies the effect of F₄₉ fault activation on grouting in the separated layer of this type of overlying rock, and determined the grouting layer, the number of drilling holes, and the principles for targeted hole arrangement. The physical and microscopic properties of fly ash used for grouting is tested and determined the selection criteria for fly ash. The physical properties of slurry made from three types of fly ash are studied, the results indicate that as the water cement ratio decreases, the specific gravity and volume concentration of the slurry made from the three types of fly ash increase. Under the same proportioning conditions, the slurry made from raw ash has the lowest specific gravity and volume concentration, while the slurry made from fine ash has the highest specific gravity and volume concentration and the slurry made from mixed fly ash has a medium specific gravity and volume concentration. The problems of high water demand for fine fly ash, high viscosity of slurry, and high settling rate of raw fly ash are solved by this method. The settling rate of the slurry made of raw ash is reduced by an average of 35.6% after 1 hour. Based on the grouting pressure and grouting flow rate, the grouting of overburden separated layer is summarized into three main stages: low pressure high flow rate, high pressure high flow rate, and high pressure low flow rate and the key grouting technologies for each stage are proposed. The research results are applied to the grouting project of the overburden separated layer in the 921103 coal mining face, through actual monitoring, the average value of surface subsidence is 243.9 mm, the injection production ratio reaches 46.1%, and the effect of grouting on reducing settlement is good.