The invention discloses an organic thin-film solar cell based on dual cathode buffer layers and a preparation method of the organic thin-film solar cell. The organic thin-film solar cell adopts a positive structure and sequentially comprises a transparent substrate, a transparent anode electrode, an anode modification layer, a donor layer, an acceptor layer, a first electron buffer layer, a second electron buffer layer and a cathode electrode, wherein the second electron buffer layer is bis-benzimidazolone (PTCBI). Through blocking of two buffer layers, the electron density of C60 and the first electron buffer layer and the polaron density of the first buffer layer and a metal cathode are reduced, excitonic quenching caused by polarons is reduced, meanwhile, energy level barrier is reduced, optical field distribution is optimized, and exciton recombination probability is prevented. By the organic thin-film solar cell, filling factor, optical current and open-circuit voltage of a solar cell are favorably improved, and finally, photoelectric conversion efficiency is improved.