The invention discloses a medium-voltage distribution network capacitor optimal configuration method and system based on reactive power division. Firstly, the medium-voltage distribution network is divided based on a depth-first search algorithm and a reactive load maximum approximation principle of each division, so that the number of nodes in each reactive power division is maximally approximated, which is favorable for optimizing compensation point position based on reactive power division. For the reactive power zoning, it is helpful to optimize the position and capacity of compensation point based on the method of cut-off optimization and range of action, which can improve the economic benefit of compensation. Finally, an actual 94-node feeder verifies the superiority and practicability of the algorithm.