The invention discloses an REO (rare earth oxide) down-conversion material full-solid organic-inorganic perovskite solar cell and a preparation method. The method comprises the steps: the preparation of an REO down-conversion nano-material, the preprocessing of a transparent conductive substrate, the preparation of an inorganic metal oxide compact layer, the preparation of an REO down-conversion nano-material porous interconnection film, the preparation of a porous structural organic-inorganic perovskite material structural layer, the preparation of a hole conductive layer structure, and the preparation of electrodes. The method employs an REO down-conversion nano-material porous support structure to replace a conventional titanium dioxide mesoporous structure, enlarges the light absorption and utilization range of the solar cell, and improves the spectrum response density and stability of the cell. The prepared solar cell is high in efficiency, is good in stability, is simple in technology, is good in repeatability, and can be used for scale production.