The invention provides an azo compound as well as a preparation method and application thereof, a dye composition and a dye as well as a preparation methods and application thereof. The azo compound has a structural formula shown in the description. The preparation method of the azo compound comprises the following steps: performing a diazotization reaction on a diazonium component so as to obtaina diazonium salt solution, and enabling a coupling component to react with the diazonium salt solution so as to obtain the azo compound. The azo compound is used as a blue dispersion dye. The dye composition comprises one or more of the azo compounds. The dye comprises the dye composition and aids. The preparation method of the dye comprises the following step: implementing commodity processing on the dye composition, the aids and water so as to obtain the dye. The dye is applied to dyeing or printing of polyester fiber, cellulose acetate fiber and blended fabrics thereof.