In this paper, we present our efforts on simulating and analyzing the effect of two-dimensional nano-sphere surface array on the characteristic of GaAs solar cells. Based on the scattering and diffraction theory of the photonic crystals, the simulation results show that the distance of adjacent nano-spheres (D) has the pronounced influence on the conversion efficiency and exhibits much poor tolerance, the absolutely conversion efficiency is reduced by exceeding of 2% as the D varies from 0 to 1 μm, in addition, the lower conversion efficiency (< 18%) is exhibited and almost remains unaltered when theD is of > 2 μm. The radius (R) of nano-spheres demonstrates much great tolerance. For D = 0, the solar cells exhibit high conversion efficiency (> 20%) and the efficiency is only varied by less than 1% whenR is varied in a very wide region of 0.3–1.2 μm. One can also find out that there is good tolerance for efficiency around the optimal value of refractive index and there is only about 0.2% decrease in final cell efficiency for around ±24% variation in the optimal values, which implys that it does not demand high precision processing equipment and the whole nano-sphere array could be fully complemented using self-assembled chemical methods.