The invention provides a thermoplastic polyolefin earthwork composite material and a preparation method thereof and belongs to the technical field of water-power engineering. The thermoplastic polyolefin earthwork composite material is used for solving the problem that the present impermeable material cannot be applied to the water-power engineering for a long time. The thermoplastic polyolefin earthwork composite material includes a thermoplastic polyolefin layer and a geo-fabric layer which are compounded with each other. The composite material has high flexibility, extensibility and durability of rubbers and excellent fusing processing characteristics of thermoplastic plastics, contains no plasticizer, has excellent ultraviolet light aging resistance, high anti-puncturing strength, high anti-burst strength, high hydrostatic pressure resistance and excellent thermal welding performance, is capable of bearing water pressure impact 200m or above, can be directly exposed and applied to the newly constructed and repaired hydraulic and hydro-power engineering for preventing seepage, such as dams, reservoirs, embankments, cofferdams, water channels, tunnels and nuclear power plants, and has the service life as same as the service life of the constructions.