The invention discloses a circuit loop polarity measuring method for busbar protection double transformation. The method comprises the following steps that: A, a component which needs to be transformed is make to be shut down; B, the current loop of the component is connected into a new busbar protection device; C, the component is made to operate again; D, the phase difference of the circuit loop of the component under a condition that the component connected into the new busbar protection device and the circuit loop of the component under a condition that the component connected into an original busbar protection device is measured through using a phase meter, if the phase difference is 0 degree, the polarity of the current loop is correct, and transformation of the component is terminated, and if the phase difference is 180 degree, the method enters step E; and E, the current loop newly connected into the new busbar protection device in the step B is inversely connected into the new busbar protection device, and step D is repeated. With the circuit loop polarity measuring method provided by the technical schemes of the invention adopted, an on-load test is not required to be performed at last, the correctness of the polarity of the circuit loop can be determined through comparing the phase difference of the polarity heads of TA secondary windings when the circuit loop of one component is connected into the busbar protection devices, and therefore, work efficiency and work quality can be greatly improved. The circuit loop polarity measuring method is applicable to the construction conditions of busbar protection double transformation.