The invention discloses a nanometer composite ceramic -coating suitable for inorganic fibers, and a preparation method thereof. The coating comprises a basic liquid and a filler, wherein the basic liquid comprises rare earth zirconate nano-powder, a nano-alumina dispersed saturated liquid, a dispersant and a polymer modified aqueous assistant; the filler comprises zirconia and alumina mixed micro-powder; and the coating concretely comprises 2-36wt% of the rare earth zirconate nano-powder, 6-52wt% of the nano-alumina dispersed saturated liquid, 0.1-4wt% of the dispersant, 1-18wt% of the polymer modified aqueous assistant, and 3-22wt% of the zirconia and alumina mixed micro-powder. The nanometer composite ceramic coating realizes super strong penetration of an inorganic fiber heat insulation material and restoration filling, cladding and binding of fiber monomers to form a three-dimensional nanometer composite ceramic protection matrix adopting the inorganic fiber heat insulation materials as a skeleton and nanometer composite ceramic particles as a filling, cladding and binding material, so penetration corrosion of high temperature, high concentration lithium and lead atmosphere (ions or gas) to the inorganic fiber heat insulation material is efficiently blocked.