The invention discloses a preparation method of a broad-spectrum infrared absorption coating. The method mainly comprises steps as follows: firstly, a thermoelectric ceramic substrate is subjected to flattening, polishing and other pretreatment, inorganic filler, a curing agent, a diluent, epoxy resin and the like are evenly dispersed and blended into epoxy resin slurry with a physical dispersion and chemical dispersion combined method, then the surface of the pretreated thermoelectric ceramic is coated with the epoxy resin slurry with a silk-screen printing or spraying method, and the broad-spectrum absorption coating is obtained after curing. The absorptivity of the coating in the band of 1.5-15 mu m is very high, is 95% or higher and slightly changes along with the change of wavelength. Besides, the coating has advantages of better thermal stability, good weather resistance and the like. The coating preparation process is simple, convenient to operate and easy to control, and the production cost can be reduced remarkably. The coating can be used as an infrared absorption coating and can be widely applied to laser energy meters, infrared sensors, thermal radiation detectors and other devices.