The identification of the fractal scale-free zone is a prerequisite for accurate calculation of the fractal dimension. The main stream of Chishui River is used as the research area. The "rough calculation" fractal dimension method is used to identify the scale-free interval of the fractal body, and the effect of the scale-free region on the fractal dimension is analyzed. The information dimension is displayed through mathematical statistics and correlation analysis. Quantitative description of river morphology. The results show that: in the calculation of a typical curved river section, when the grid side length r = 40, the point distribution of the coarse fractal dimension of the water edge line in 70% of the river section is unstable, and the geomorphic area of ??50% of the river section is roughly calculated. The instability of the dimensional value point distribution occurred. After verification by the correlation coefficient method, it was determined that [10,40] is the unscaled area of ??the information dimension measurement; the information corresponding to the increasing grid edge length r in the unscaled area. The difference between the quantities tends to a certain constant. The time difference for calculating the water dimension information dimension tends to be 0.18, and the time difference for calculating the geomorphic area information dimension tends to 0.3. The water edge information of the curved river section measured by the main stream of Chishui River The dimensional interval range is [0.9157, 1.0421] with an average value of 0.9979, the morphological area information dimensional interval range is [1.3013, 1.9230] with an average value of 1.6760, the curvature ratio range is [1.0259, 2.6512] with an average value of 1.2712; In the middle and lower reaches of the river, the correlation coefficients between the waterline information dimension and the curvature rate are 0.469 and 0.644 in turn, and the significance is gradually strengthened. The correlation between the information dimension of the landform area, the curvature rate, and the waterfront information dimension is relatively higher throughout the main stream. Weak and negatively related to the waterline information dimension.