The invention discloses blue reactive dye. The structure of the blue reactive dye is shown as a formula I, and a definition of each substituent group is defined in the description. The blue reactive dye has high solubility in a non-aqueous medium and high affinity to cotton fibers, and the cotton fibers can be dyed at a high dying rate; at the same time, the corresponding part, which is not fixedto the fibers, of the hydrolyzed dye is very easy to remove.