Due to the influence of pore characteristics(porosity, variability and complexity) on rain infiltration, the microscopic pore characteristics of fine clay in eluvial gravel soil with representative grade of a slope in Zhaoshan Zone in Xiangtan City of Hu'nan Province were studied through image processing technology. The results show that there is a quadratic curve relationship between porosity and moisture content in fine clay particals under the same quality, and the experiment soil has the best compaction when the moisture content is 10.41%; the pore number, the pore tested and the pore variability decreases with the increase of the moisture content variation degree, its indicate that the smaller of the pore moisture content, the higher level of distortion and the more complex of pore, and the more pore number, the more beneficial to infiltration for surface water; the pore orientation angle under different moisture content are concentrated in 10°~20°, 50°~60°, 100°~110°, and 140°~150°, and the less moisture content, the more obvious pore directionality is; the distribution of the pore's angle shows a radial structure, and the description is most evident when the moisture content is 15%, and is advantageous to the level osmosis migration of moisture.