The invention is a centrifugal casting radiant tube coating and a preparation method thereof, the coating comprises the ingredients (mass percent) of: 25-30% of diatomite of, 5-10% of zircon powder, 1.0-1.2% of titanium powder, 1.5-1.8% of iron powder, 4.5-5.0% of sodium bentonite, 2.0-2.5% of polyvinyl alcohol, 0.8-1.0% of sodium alginate, 3.5-4.0% of silica sol, 0.8-1.0% of sodium dodecylbenzene sulfonate, 0.05-0.08% of silane and 46.82-49.95% of water, wherein, the mass percent of the diatomite and the zircon powder is not less than 35% and not more than 37%, the mass percent of the titanium powder and the iron powder is not less than 2.7% and not more than 2.9%, and the mass percent of the sodium bentonite plus the polyvinyl alcohol plus the sodium alginate is not less than 8.0% and not more than 8.2%. The inventive coating is used for the centrifugal casting radiant tube after dry-blending, mixed grinding and sieving, uniformly distributed bulges (namely pitting surface) can be formed on the outer surface of the radiant tube to improve heat efficiency of the radiant tube. The inventive coating also has excellent adhesive force, high temperature strength and crack resistance, thus reducing defects on the surface of the radiant tube and improving quality of complex tube. Using the inventive coating to cast the radiant tube can result in remarkable economical benefit.