The invention provides a mono-azo compound represented as the formula (I), and a preparation method and an application thereof. The mono-azo compound, as a disperse dye, is applied to dyeing and printing of polyester and blended fabrics thereof, especially a polyester-spandex blended fabric, has excellent deep-dyeing property, light fastness, sublimation fastness and washing fastness and is suitable for being compounded with other high-washing fastness disperse dyes so as to produce high-fastness disperse dye in different tones. Especially, the compound is suitable for being used as a component of blue, navy blue and black colors.