The invention relates to a blue disperse dye monomeric compound and a preparation method and application thereof. The structural formula I of the compound is shown in the description. The preparation method is performed in a diazotization and coupling reaction mode. The blue disperse dye monomeric compound is independently applied to preparing disperse dye or being combined with other dye monomers for preparing disperse dye. The preparation method is simple in technology and low in cost and is used for preparing the obtained dye, and the dye has the advantages of being good in repeatability, and good in color fastness to rubbing, color fastness to washing, color fastness to light and elevating power.