In order to study the effect of light intensity uniformity on the conversion efficiency of GaAs cells, based on the working principle of single junction GaAs cell, the photoelectric conversion efficiency of GaAs cells was analyzed when the laser intensity was different by using the equivalent circuit, and the conversion efficiency of GaAs cells in different light intensity uniformity was studied by experiments. Results show that the light intensity uniformity has a great influence on the photoelectric conversion efficiency of the single junction GaAs cell. In some extreme conditions, it may cause the hot spot effect and completely destroy the GaAs cells.