The invention provides a green fluorescence cyanine dye, which has a structural general formula I shown in the specification, wherein in the formula, X is C(CH3)2, O, S or Se; R1 and R2 are independently selected form H, C1-18 alkyl groups, OR6, C1-6 alkyl group OR6 or halogen respectively; R3 is N(R5)(R7); R4 is selected from C1-18 alkyl groups, benzyl groups and substituted benzyl groups; the substituted benzyl groups are arbitrarily substituted by the following groups: C1-18 alkyl groups, CN, COOH, NH2, NO2, OH, SH, C1-6 alkoxy groups, C1-6 alkyl amino groups, C1-6 acylamino groups, halogen or C1-6 halogenated alkyl groups; R5 and R7 are independently selected from H or C1-18 alkyl groups respectively; R6 is H or C1-18 alkyl groups; and Y is negative ions. The fluorescence dye can be used for DNA (Deoxyribonucleic Acid) quantitative detection and biological dyeing, and is applied to the fields of nucleic acid marking, blood cell analysis, clinic medical diagnosis, immune analysis detection and the like.