Abstract: Three bi-functional reactive yellow dyes containing fluoro-triazinyl groups, which were based on 2-aminonaphthalene-1, 3, 6-trisulfonic acid as the diazo components and m-urido-aniline as the azo components, have been studied. Their UV-visible absorption spectra, dyeing character parameters and wet fastness have been evaluated comparing with reactive yellow dye C.I.176. The relationship between dye structures and their dyeing properties are investigated. It shows that the reactivity of fluoro-triazinyl reactive dye is much higher than corresponding chloro-triazinyl reactive dye, owing to the strong withdrawing electron effect and easily leaving of fluorine atom. Different substituent groups on triazinyl ring can affect the planar and linear structure of molecules, thus causing change the performance parameters of dyes. In addition, the effect of different substituent on chromophore can be predicted by micro-perturbation MO theory.