The invention discloses a method for optimizing the position of a sensor in a modal test of an on-load tap changer. The method comprises the steps of firstly, based on a mode calculation result of anon-load tap changer finite element model, obtaining all-order frequencies and all-order vibration modes of a test model; and then, by taking an effective independence-driving point residue method as an optimization method and a stepwise reduction method as a searching method for an optimal measuring point, performing iterative loop until a required quantity of measuring points are selected out. Inthe optimization method, a traditional effective independence method is abandoned, and the improved effective independence-driving point residue method is adopted; in the searching method, a traditional direct method is improved, and the stepwise reduction method is provided. A new method is provided for optimizing the position of the sensor in the modal test of the on-load tap changer; and the method is simple and easy to implement and easy to understand, and can be widely applied to other electrical equipment.