Quantum dots (QDs) can modulate the solar spectrum through the down-conversion mechanism to better match the spectral response of solar cells. Following previous work, this paper first tested the response of QD solar cells to specific monochromatic light, and found that QDs can effectively improve the photoelectric conversion efficiency (PCE) in the ultraviolet (UV) band by comparison. Then the photoelectric properties of the QD solar cells are tested under the air-mass 1.5 (AM1.5) and air-mass 0 (AM0) spectra. The experimental results show that because the absorption band of QDs is in the UV region, the space solar cells in the AM0 spectrum can obtain better PCE after coating QDs. The research results show the technical route of space solar cells with down-conversion mechanism, and put forward an important direction for the application of space solar photovoltaic (PV) technology, and have a good application prospect.