The shot-to-shot variation of laser fluence spatial distribution on a large-aperture high-power laser facility is statistically analyzed. Statistical results show that the maximum fluence spatial distribution to which any location in the optic beam will be exposed after N shots, can be described by Gaussian function, and the average fluence across the beam increases with laser shots while standard deviation is relatively constant, independent of laser shots. This is due to the fact that laser fluence spatial distribution possesses similarity over the whole beam and dissimilarity at local positions for different laser shots.