The present invention provides a group of water-soluble sulfur dye having carboxyl groups. For the kind of dye, a sulfur dye is first reduced to a leuco compound by sodium sulfide, and the leuco compound reacts with an active compound containing carboxyl groups to obtain a water-soluble sulfur dye containing the carboxyl group. The water-soluble sulfur dye provided by the present invention is applicable to dying of cotton, wool, silk, and leather. Being both water-soluble and carboxyl group reactive, the product has a simple application process and desirable color fastness, thereby having broad application prospects.