The invention discloses a solar cell with a composite dielectric passivation layer structure and a preparation process thereof. A silicon oxide film, an alumina film and a silicon nitride or silicon oxynitride film are deposited in turn on the front, back and sides of a p-type silicon substrate to form a composite dielectric film on the whole surface, and windows are opened locally to lead electrodes out. Through aluminum oxide, silicon dioxide, silicon oxynitride, silicon nitride with different refractive indexes and a back surface passivation layer with a laminated structure of the materials, the back surface recombination rate is greatly reduced, the back reflectivity is improved, the CTM of a module is reduced, and the light attenuation and heat-assisted light attenuation and the anti-PID performance of the cell are improved. The structure can be made on a boron/gallium-doped p-type monocrystalline silicon, p-type polycrystalline silicon or p-type monocrystalline-silicon-like substrate, and a passivation method based on the composite dielectric film passivation structure can be used to manufacture PERC cells, double-sided PERC+ cells and imbricate PERC cells. Based on the preparation process steps and sequence, the corresponding preparation mode and the process parameter range of the laminated structure, the making of the cell can be well completed.