The invention relates to slurry for a micro-engine thrust chamber and a preparation method and application of the slurry and belongs to the technical field of two-component liquid rocket orbit/attitude control engines. The thrust of a micro-engine ranges from 0.1 N to 5 N, the throat diameter of the micro-engine thrust chamber ranges from 0.3 mm to 1.0 mm, and a spray pipe on the micro-engine thrust chamber is made of niobium-tungsten alloy. The slurry is stable in performance and uniform in ingredient, the concentration of the slurry is adjusted, when the micro spray pipe with the throat diameter below 1 mm is coated with a coating through the slurry, the throat portion is not likely to be blocked, and meanwhile the coating thickness of the coating can be guaranteed. After the inner surface and the outer surface of the spray pipe of the micro thrust chamber with the throat diameter below 1 mm are dip-coated with the slurry, the high-temperature oxidation resistance of the spray pipe is guaranteed, and meanwhile the throat diameter of the spray pipe can meet design requirements.