The invention relates to a low-loss threshing control system and a low-loss threshing control method for a corn harvester, and belongs to the field of agricultural automation. The low-loss threshing control system comprises a CAN bus, a measuring transmission device, a display, a button board, an operating handle, a controller and an executing mechanism, wherein the executing mechanism comprises aworking speed controlling hydraulic motor connected with a working speed controlling electrohydraulic proportional valve and a working speed controlling variable pump, a threshing drum speed controlling speed-regulating motor and a concave clearance controlling distance-regulating motor; the measuring transmission device comprises a grain breakage detection module, a working speed sensor, a threshing drum speed sensor and a concave clearance sensor. The low-loss threshing control system can complete electric control and manual adjustment of working parameters, can also make decisions according to the harvesting quality, the crop state and the machine running state in the corn harvesting process to intelligently regulate and control the threshing drum speed, the concave clearance and the working speed, so that the working parameters are closely coordinated to be adapted to influence from a harvesting working environment, the crop state and the like so as to improve the harvesting quality and the working efficiency of the corn harvester.