In order to slove the problem that the representative particle size method is difficult to accurately quantify the roughness of the gravel bed surfaces (GBS), the statistical theory was introduced to study the roughness properties of natural GBS. A series of loose-stacked GBS were prepared by using particles with different size and composition. Based on the analysis of the laser scanning data of the above GBS and the existing test results, the relationship between the statistical parameters of bed roughness and particle size was discussed, and the elevation variation characteristics of gravel bed profiles (GBP) and GBS was analyzed. The results showed that the frequency distribution of bed elevation had a negative skewness, the curve shape was steeper than the normal distribution, and the kurtosis Ku is greater than 3 which belongs to high narrow peak. The standard deviation σz increased with the increase of the median particle size d50, and the skewness Sk decreased with the increase of d50. In the case of the same particle size d50, the standard deviation σz and skewness Sk of unworked GBS were less than that of water-worked GBS, but there was no significant difference in kurtosis Ku. The one-dimensional structure function of GBP satisfied the variogram spherical model, whose parameters included the range, nugget and abutment value. The range showed a trend of first decrease and then increased with the increase of d50 and σz, and nugget and abutment value increase with the increase of d50 and σz. The trend couied be fitted with second order polynomial curves. The distribution pattern of two-dimensional structure function was closely related to sampling scale hx and hy. When hx, hy and d50 were equivalent, the distribution of the two-dimensional structure function was close to the circular shape and the rough GBS was isotropic, with the distribution law of the structural function being consistent with that of the water-worked GBS. With the increase of hx and hy, the complexity of the distribution of the two-dimensional structure function was enhanced obviously. The structure function values of different quadrants were different, and there was no longer the distribution law of the water-worked GBS and the rough GBS was anisotropic.