Abstract: In order to prepare low cost filling materials to meet the requirements of green coal mining technology proposed in the pilot green mining in Shanxi Province, such as popularize filling materials according to local conditions and coal gangue did not rise to the well, composite filling materials of high water fly ash were prepared by using waste mineral resources such as fluorogypsum, fly ash and coal gangue, and the slump, bleeding rate and mechanical properties of the materials were studied; the composition and microstructure of hydrated mineral were studied by means of XRD and SEM; the mechanical properties of composite materials were simulated by molecular dynamics software. The research results show that the material has good fluidity and high strength growth rate, and the compressive strength of 28 d can reach 4.96 MPa; microscopic observation shows that the composite material is dense and has few porosity; the cost of composite materials is as low as 78 yuan/m³; the composite molecular model is simulated under the NVT ensemble, the elastic modulus of calcium silicate hydrate is higher than ettringite, and with the increase of calcium silicate hydrate, the mechanical properties of composite materials are better.