The invention discloses a CMT and laser cladding composite repair method for an inner hole of a flat head sleeve of a rolling mill spindle. The composite repair method comprises the following steps ofcutting the inner hole of the flat head sleeve to be repaired; removing a wear fatigue layer; cleaning the machined surface and removing impurities on the machined surface; using a CMT process to surfacing a transition layer on the machined surface; detecting the defects of a CMT welding layer, such as cracks; preparing alloy powders and cladding with a CW fiber laser, and coloring the surface ofa laser cladding layer to detect the detects, such as the cracks; and machining the laser cladding layer surface to obtain the flat head sleeve, specifically, the size, the tolerance and the surfacefinish of the flat head sleeve meet the requirements of a drawing. According to the CMT and laser cladding composite repair method for the inner hole of the flat head sleeve of the rolling mill spindle, a CMT welding process and a laser cladding process are organically combined, so that the purposes of low cost and agile repair are achieved; and the hardness and alloy compositions of the laser cladding layer can be quickly adjusted according to the change of working conditions, so that the service performance of a product is significantly improved and the service life of the product is significantly prolonged, and the service life is prolonged by more than two times