Reactive navy blue RGB azo dye and a preparation process thereof are disclosed, and the structural formula showed as right formula, wherein R1=H, SO3H, OCH3, CH3, C2H5, OC2H5, and M=Na, K. The compound is prepared through coupling H acid with diazonium salt of sulphate ethyl sulphone aniline compound which comprises sulfonic acid group or methyl group, methoxyl group, ethyl group and ethoxyl group. The dye is suitable to be used on the dying, direct printing and discharge of cotton fiber, and has the advantages of evenly coloring, bright color, excellent fastness, favorable lifting power, high color yield and extreme high fixation yield.