The invention discloses a gear variation tracking-based extra-high voltage on-load tap changer protecting method. According to the method, gear information is connected into an on-load tap changer protecting device, so that the on-load tap changer protecting device can automatically track the gear variation of an on-load tap changer and automatically change differential current calculation modes of the on-load tap changer in real time. The gear information is connected into the on-load tap changer protecting device, and the differential current calculation modes are automatically adjusted, and therefore, fixed value interval setting and fixed value setting can be simplified; a more complete and simper processing method can be provided for protection for an extra-high voltage on-load tap changer; main protection loss of the on-load tap changer caused by differential protection sensitivity reduction and differential protection quit of the on-load tap changer in an on-load voltage regulation process can be avoided; manual intervention is not required in a gear regulation process; and the operation of operating workers can be greatly simplified. The gear variation tracking-based extra-high voltage on-load tap changer protecting method has the advantages of simplicity, practicability and easiness in realizing microcomputer-based protection, and can improve the reliability of the protection for the extra-high voltage on-load tap changer.