The invention relates to an optimal segmentation method and apparatus for a power distribution network line. The optimal segmentation method comprises the steps of obtaining a topological structure of a to-be-segmented power distribution network line, and correlation parameters of the power distribution network line; inputting the topological structure and the correlation parameters into a preset power distribution network line optimal segmentation model, and performing variable assignment on nodes which are not allowed to set a section switch and nodes which need to set section switches for sure in the power distribution network line; and under set constraint conditions, calculating the number of segmentation and segmentation length of the power distribution network line through the power distribution network line optimal segmentation model. By virtue of the optimal segmentation method and apparatus, the two variables, including the number of segmentation and segmentation length, can be solved at the same time, so that the scheme is convenient and simple.