Spatial distribution characteristics of soil C/N ratio and its affecting factors at a county scale in hilly area of Middle Sichuan Basin were analyzed based on field sampling. Result indicated that soil C/N ranged from 4.84 to 21.79, with a mean value of 11.93. The coefficient of variation was 26.3%, which suggested soil C/N had moderate variability in this study area. The ratio of nugget to sill was 73.0%, which suggested the spatial variability of soil C/N was determined by both structural and random factors, and the random factors played a more important role. The soil C/N was higher in northeast and southwest while the central part of the study area was characterized by relatively lower values of soil C/N. The soil C/N ranged from 10.0 to 13.5 in most parts of the study area. Parent material, soil type, topographic factors and land use type had significant impacts on soil C/N (P<0.05). Soil C/N showed a significant positive correlation with elevation and slope (P<0.05). The soil parent materials were able to explain 8.7% of soil C/N spatial variability. The explanatory power of soil group, subgroup and soil genus were 3.8%, 5.0%, 8.7%, respectively. Topographic factors showed the lowest explanatory power of only 0.8%. However, land use type could explain 23.9% of the spatial variability, which suggested that land use type was the dominant factor in controlling the spatial variability of soil C/N.