The invention discloses an on-vehicle easy-maintenance voltage transformer error calibration system and a method thereof. The on-vehicle easy-maintenance voltage transformer error calibration system and the method belong to the technical field of mutual inductor testing. The on-vehicle easy-maintenance voltage transformer error calibration system provided by the invention comprises an on-vehicle platform on which a standard voltage transformer, a test booster and a test box are arranged. The standard voltage transformer is an infrared epoxy barrel type standard voltage transformer. The test booster is an infrared epoxy barrel type standard test booster. A voltage regulating control power supply is fixedly arranged in the test box. The test box is internally provided with a mutual inductor calibrator, a voltage load box, a remote controller and a connecting line. A multi-combined compensating reactor is arranged in the voltage regulating control power supply. The error calibration system provided by the invention can be used for field calibration of a 500kV-220kV voltage transformer. The height of on-vehicle system in a transportation state is only 2.2m. The on-vehicle easy-maintenance voltage transformer error calibration system has advantages of facilitating mobile transportation and traceablility maintenance, realizing high safety and high efficiency in use, and obtaining high stability and high reliability of the error data of the standard voltage transformer.