A Ni-Co-Cr-Al-W-Ta-Mo based high-entropy high-temperature alloy and a preparation method thereof are disclosed and belong to the field of high-entropy alloys. The chemical composition of the alloy isNiCoCr<c>Al<d>W<e>Ta<f>Mo<g>Rx, wherein R is one or two of Re and Ru. The method includes removing surface oxide skin of raw material metals by utilizing a mechanical-chemical combined process;cleaning the raw material metals by utilizing industrial ethanol and utilizing ultrasonic shaking; smelting the alloy by using a vacuum arc furnace; charging industrial argon when the vacuum degree is5*10<-2> Pa; after a master alloy is uniformly melted, injecting the alloy into a water cooling copper mould by utilizing a vacuum casting or suction casting device to obtain a high-entropy alloy rod; performing solution treatment at 1250 DEG C for 2-6 h; and then performing ageing heat treatment at 900 DEG C and 950 DEG C for 4-50 h. The disclosed alloy has excellent room-temperature and high-temperature strength, excellent resistance to high-temperature oxidation, and excellent creeping resistance, fatigue resistance and long-term tissue stability, is suitable for manufacturing hot end elements, such as blades and turbine discs, of aero-engines and gas turbines, and is used for engineering machines, special vehicles, coal, ore, railroads, and the like.