In order to accurately grasp the soil fertility in Three Gorges Reservoir Region after changing mountain slope into terrace field, we take Wushan County for example, and use the spatio-temporal substitution method to analyze the soil nutrient status and trend about the terrace field changed from mountain slope under different length of implementation. The results show that the soil fertility is generally low in the study area, and according to the soil nutrient grading standards in the second national land survey, the average content of total nitrogen, available potassium, organic matter and available phosphorus reaches Standard III, Standard III, Standard IV and Standard V, respectively, and the spatial heterogeneity of soil nutrients is small. Compared to the sloping land, the terrace field changed from mountain slope has increasing soil nutrients on the whole with the length of farming. The mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 2 years is lower than in the sloping land, and there is the biggest difference in soil fertility, while the mean of various indicators about soil nutrients in the terrace field changed from mountain slope for 14 years shows a linear upward trend, and the difference in soil fertility decreases.