Abstract: For the occurrence of accidents such as crushing of rock mass under the coal mine and roof caving and rib spalling, the polyether polyol, polymethylene polyphenyl isocyanate, fly ash, flame retardant TCPP, silane coupling agent are used as the basic raw materials, and the original polymerization is carried out. The Polyurethane and fly ash reinforcing material was prepared by the original flavor polymerization method. On this basis, the optimal amount of fly ash and the amount of 3-methacryloxy-propyl trimethoxy silane (MPS) additive were explored. Under the optimal conditions, the microstructure and particle size distribution of PU/FA composites were studied and compared by scanning electron microscopy and particle size analyzer. At the same time, the effects of compressive strength on PU, PU/FA-0% and PU/FA-2.5% reinforcement materials under different curing time were studied. The results show that the fly ash can be effectively filled into the polyurethane matrix and the strength is optimal when the content is 20%. Adding 2.5% MPS can not only effectively promote the refinement of the fly ash particles and the dispersion in the polyurethane matrix. It can further improve the interfacial properties and crosslink density between the inorganic fly ash and the organic polyurethane.