The invention discloses a distribution network line switch position setting method based on an impedance change law. The method comprises the following steps: (1) a wire path and a through wire are selected according to distribution network wire information; (2) the change law of impedance along the through wire and the wire path is calculated; (3) according to the impedance at the tail end of thethrough wire and the system impedance at a 10 kV bus, a criterion is used to determine the number of switches arranged on the line and the impedance values at the setting positions; and (4) accordingto the wiring condition of the wire, one impedance value at a switch setting position is converted to a certain pole number on the line, and the impedance value at the switch setting position is updated. The invention provides a scientific and effective method for distribution network line switch position setting, and a decision-making guidance is provided for enabling a distribution network linedesign department to develop a line design plan and an operation and maintenance department to verify and improve the rationality of switch setting on the distribution network line.