The invention discloses pre-coated sand with high strength and a low gas evolution rate and a preparation method thereof. The pre-coated sand with high strength and low gas evolution rate is prepared from the following raw materials in parts by weight: 60-80 parts of quartz sand, 15-20 parts of celestite, 5-10 parts of wollastonite, 0.4-0.8 parts of ethenyl tri(beta-methoxyethyoxyl) silane, 4-6 parts of pentaerythritol oleate, 3-5 parts of epoxy soybean oil, 2-3 parts of nano magnesium oxide, 0.5-1.5 parts of bisphenol A epoxy resin, 1-2 parts of thermosetting phenol resin, 3-6 parts of diaminodiphenyl methane, 5-10 parts of urotropine, 4-8 parts of calcium stearate and 3-5 parts of composite powder. Compared with the conventional pre-coated sand, the pre-coated sand disclosed by the invention is not only high in strength, good in heat resistance, good in mobility and small in roughness, but also good in gas permeability and low in gas evolution rate, so that a casting piece can be effectively prevented from generating defects such as pin holes, nitrogen gas holes and burnt-on sand, and therefore, the yield of the casting piece is greatly improved.