The invention discloses a high-crack-resistance building waterproof material and a preparation method thereof. The high-crack-resistance building waterproof material is prepared from the following raw materials in parts by weight: 30-50 parts of polyether tribasic alcohol, 10-15 parts of petroleum asphalt, 5-10 parts of fluorocarbon resin, 8-15 parts of nano magnesium oxide, 12-15 parts of organic silicon modified epoxy resin, 12-18 parts of aluminum potassium sulfate dodecahydrate, 15-25 parts of hydroxyethyl cellulose, 4-9 parts of Portland cement, 10-20 parts of talcum powder, 2-10 parts of polyoxyethylene, 1-8 parts of magnesium stearate, 11-17 parts of acrylate, 2-8 parts of steel slag micropowder and 1-8 parts of trimethyl trimellitate. The high-crack-resistance building waterproof material integrates the heat-insulating property and waterproofness, has the advantages of higher compression resistance, long service life, favorable high-temperature resistance, certain elongation percentage, high crack resistance, low cost, favorable binding property, low oxidation and aging tendency, high tensile strength, favorable waterproof effect and the like, can form a waterproof layer on the object surface to effectively avoid the object oxidation, and can be used as a waterproof material for interior architecture. The high-crack-resistance building waterproof material has the advantages of simple formula, low cost and favorable properties, and is suitable for large-scale production.