Disclosed are a control system and a control method for automatic gear shifting of a loader. The control system is characterized by being provided with a microprocessor. The microprocessor is used for receiving signals of engine speed, torque converter turbine speed, loader speed, operation hydraulic system pressure, braking pressure, gears and a steering handle. The microprocessor is provided with a driver's intention judgment controller, a gear operation controller and a gear shifting time controller. The control system has the advantages that three control links are provided, input signals are analyzed first to judge a driver's intention so as to decide shifting gear or not, the control links are selected via gear shifting strategies to select a proper gear shifting process, and finally, gear shifting time of former-gear disengaging and later-gear engaging is determined through the gear shifting time control link, so that gear shifting smoothness, power continuity and oil consumption reduction are guaranteed, and comfortable, energy-saving and efficient control is realized.