The present invention provides a self-adaptive control system for feeding mouth opening of a round bale bundling machine and a controlling method thereof. The self-adaptive control system comprises a feeding device, a rotary coder, a displacement sensor, a hydraulic regulation system and a controller, wherein, the input end of the controller is electrically connected with the rotary coder, the displacement sensor, a first oil pressure sensor and a second oil pressure sensor respectively, and the output end of the controller is electrically connected with a solenoid directional valve via an interlocking controller； the controller takes the bearing force of piston rods and the rotation speed and the rotation speed change rate of a feeding knife roller as input variables and takes the positions of the piston rods as an output variable, to establish a fuzzy control model of the feeding mouth opening of the feeding device, the extension and retraction of the piston rods in a left oil cylinder and a right oil cylinder under hydraulic driving are regulated actively by controlling a three-position four-way solenoid directional valve, and thereby self-adaptive control of the feeding mouth opening is achieved, instable baling performance resulted from non-uniform feeding amount is alleviated, a jamming fault of the feeding knife roller incurred by sharp increase of the feeding amount is avoided, the service life of the feeding component is prolonged, and the overall operating efficiency and reliability of the machine are improved.
