The invention relates to the field of solar cells, and particularly provides a preprocessing device and preparation equipment of a buffer layer and a solar cell and a preparation method thereof. The preparation method of the buffer layer comprises the steps that the solar cell back electrode covered by the absorbing layer is vacuumized and then immersed in water, and then the deposition reaction liquid is injected so that the buffer layer is formed on the surface of the absorbing layer through chemical bath deposition. With application of the preparation equipment of the buffer layer, the photoelectric conversion efficiency of the corresponding solar cell can be significantly enhanced.