The relationships were studied by UV-visible spectrophotometry method among the structure of reactive blue X-BR, reactive blue K-3R, reactive blue KN-R, reactive blue M-BE, reactive blue M-2GE, reactive blue EF-3G and their colors, poplar dyeing characteristic parameters — S, E, R and F values, exhaustion curves and fixation curves. The results show that the longer the length of reactive dye chromophore of conjugated system was, the more coordinating role of donating and withdrawing electron groups had, the smaller the space steric hindrance w...