A safety working range based (N-1) calibration method for a main transformer of a medium-voltage power distribution system comprises the following steps of inputting structural information of the medium-voltage power distribution system for carrying out topological structure analysis on the medium-voltage power distribution system and carding a connection relation among circuits; carrying out wiring mode analysis on the medium-voltage power distribution system; reading information of a working point of the medium-voltage power distribution system; giving out a safety boundary of a safety working range of the main transformer of the medium-voltage power distribution system; calculating safety distance from the working point of the medium-voltage power distribution system to the safety boundary of the safety working range of the main transformer; judging a running state of the working point of the medium-voltage power distribution system; and giving out a (N-1) calibration result of the main transformer in a research region. According to the calibration method, the working point of the conventional power distribution system can be described from the perspective of a grid structure of the power distribution system and based on a feeder interconnection relation, the boundary of the safety working range of the main transformer of the medium-voltage power distribution system is further described, and the safety distance from the working point of the system to the boundary of the safety working range of the main transformer is calculated. By the calibration method, more comprehensive safety information can be provided, and the calibration method is more suitably used in real-time dispatching operation.