The invention belongs to the field of mechanical transmission and provides a split flexible gear and a gear pair. The split flexible gear comprises a gear ring, a hub and a connector, the gear ring comprises a rim, gear teeth and a radial plate, the hub and the radial plate are in detachable connection through the connector, and one lateral side of the radial plate is bent to form an unloading cavity. By adoption of the structure, the radial plate is flexible and capable of deforming under stress to reduce engagement misalignment quantity of the gear teeth when the gear in engagement loading, and accordingly modification quantity in gear design is reduced, the larger the load, the larger the misalignment quantity in engagement, and the larger the deformation quantity of the split flexible gear, the larger the gear engagement misalignment quantity reduced by deformation quantity of the radial plate, so that engagement misalignment quantity difference values of the gear under various operating conditions are decreased, loading uniformity of surfaces of meshed gears under each operating condition can be guaranteed through modification aiming at the gear engagement misalignment quantity, and gear strength and reliability are improved.