Abstract: The influence of laser spatial coherence on illumination uniformity is studied in this paper. Partially coherent Gaussian beam is expanded into an independent superposition of Hermite-Gaussian modes. The coherence length of partially coherent Gaussian beam can be derived from its M2 factor. The larger the M2 factor, the shorter the coherence length. Propagation of laser beam through atmospheric turbulence is treated with phase screen approximation. The uniformity of illumination beam is expressed by s 2I . s 2I of partially coherent beams with different M2 factor is computed after propagation through atmospheric turbulence. Th e results of numerical simulation show that illumination uniformity is improved with the decrease of illumination laser spatial coherence.