The invention discloses a formula for a reactive dip-dying dye, wherein the formula comprises the components in parts by weight: 40-60 parts of a 2,4-difluoro-5-chloropyrimidine dye, 50-80 parts of avinyl sulfone dye, 40-80 parts of an alpha-bromoacrylamides reactive dye, 8-12 parts of a dye leveller peregal, 10-14 parts of sodium sulfate, 12-16 parts of sodium chloride, 8-14 parts of disodium hydrogen phosphate, 20-60 parts of sodium dihydrogen phosphate, 15-25 parts of sodium hydroxide, 20-90 parts of sodium carbonate, and 15-25 parts of urea. The reactive dip-dying dye has the advantages of high fastness, high wet fastness, bright color and luster, excellent performance and high applicability, and is a dye having both the hue and the performance adapting to requirements of the market on fibers and clothing materials.