Studying the scale effect of cultivated land fragmentation is of great significance for remote sensing monitoring, remediation and sustainable use of cultivated land in mountainous areas. This paper selects three types of typical landforms with different geomorphological backgrounds as the case area, namely, Sunjia village in the dam area, Yayu village in the hilly area and Xiaoba village in the mountain area. The fragmentation measurement model is constructed to quantitatively analyze the scale effect of the degree of cultivated land fragmentation at the five resolutions of 0.1 m, 1 m, 2 m, 5 m and 10 m in Guizhou mountainous areas. The main conclusions are as follows: (1) with the decrease of image resolution, the characteristics of cultivated plots under different landscapes have obvious scale effects. (2) There are differences in the degree of cultivated land fragmentation under different geomorphological backgrounds. The fineness of the hilly area is the highest, followed by the dam area, and the mountain area is the lowest. The degree of cultivated land fragmentation at different image resolutions has obvious scale effect, and the index of cultivated farmland fragmentation in all the three typical villages show a power function decline. In addition, the degree of cultivated farmland fragmentation with different geomorphological backgrounds is different in response to scale changes. The grain size response of cultivated land in the dam area is the strongest, followed by the hilly area and that of the mountain area is the weakest. (3) With the previous scale as a reference to calculate the loss accuracy, the degree of cultivated land fragmentation in the dam and hilly areas is the most sensitive when the image resolution is changed from 2 m to 5 m, while the sensitivity of the mountain area to the scale change is increasing. When the basic scale is used as the reference, the degree of cultivated land fragmentation in the hilly area is the most sensitive to the scale change, followed by the mountain area, and the lowest is in the dam area. The study aims to provide reference for the investigation, evaluation and treatment of cultivated land fragmentation in mountainous areas.