A dye whose chemically active radical groups react chemically with fibers is named as Reactive dyes, or reactive dyes. Invented by the British company, Imperial Chemical Industries, first in 1956, most of the Reactive dyes dissolve in water, and the molecular structure includes parent dyes and active groups. The general structure can be represented by W-D-B-Re where D is a chromogen; B is an active group and a chromogenic coupling group; Re is an active group; W is an aqueous solution. Parent dyes include dyes with the structural types as azo, anthraquinone, phthalocyanine, trimethoprim and so on, and active groups includes types of triazine, vinylsulfone, quinoxaline, pyrimidine and acrylamide. Among them, output of triazine and vinylsulfone Reactive dyes are the largest such as reactive brilliant red X-B and reactive brilliant Orange KN-4R.

It contains groups that can react with fiber in molecule of Reactive dyes. Chemical reactions occurred between dyes and fibers during the procedure of dyeing and generated new covalent bonds, thus greatly improving the color fastness, especially wet fastness. Reactive Dyes, applied for a variety of fibers such as cotton, linen, rayon, wool, silk and blended fabric for dyeing and printing, are easy to use, and own bright color and the chromatography is more complete with lower cost. When dyeing, it is accompanied by hydrolysis of the Reactive dyes. Thus, in addition to the dye, solid color, there is post-processing stage in order to fully wash hydrolyzed dyes. Dye fixing rate is generally no more than 70% and to improve it, there occurs Reactive dyes with a composite activity groups (molecules containing two or more active groups) in recent years, whose fixation rate is of 85% to 95%.