A method for casting a box-type complex water-cooling exhaust pipe by using an iron mold coated sand is disclosed. By using the water-free coated sand mold, the method helps to realize rapid cooling and mold filling, eliminate the defects of nail-passing-hole structure loosening and casting deformation often happening in the water-cooling exhaust pipe; and the prepared water-cooling exhaust pipe has higher tensile strength, higher hardness, better graphite morphology and better graphite grade, and the amount of stable pearlites is 98% or more. The yield of castings is improved from 54% to 96% or more. The finished product is good in texture compactness, good in texture refining capability, good in surface quality, and stable and reliable in quality. Also, during the production, the method has the advantages of being small in use level of the sand and paints, small in equipment investment, small in equipment occupied area, high in production efficiency, low in manufacture cost, good in environmental protection property, wide in prospect, and applicable to production of various engine exhaust pipes with high quality demands and complex thin-wall double-layer walls.