The invention provides an anthracene-based organic dye and a preparation method thereof. The organic dye provided by the invention has a structure of formula (I) or formula (II), wherein Ra, Rb, and R2-1 to R2-4 are as defined herein. The organic dye provided by the invention is obtained by modifying an anthracene with Ra and Rb or modifying anthracene-based groups decorated with an aryl group or a heteroaryl group with Ra and Rb, thereby the power conversion efficiency of a dye sensitized solar cell is significantly improved when the organic dye prepared according to the present invention is applied in a dye-sensitized solar cell. Furthermore, the preparation method of the organic dye according to the present invention is quite simple together with abundant raw materials and low cost, making it possible to be commercialized.