The invention provides a replaceable reinforcing method for a girder structure. The method specifically comprises steps as follows: Step 1, a girder to be reinforced is cleaned and flattened, and a position is designed at the bottom of the girder for drilling; Step 2, a chemical anchor bolt is embedded in a hole, reserved for mounting of a carbon fiber plate, in the bottom of the girder, a carbon fiber plate tension device and a carbon fiber plate assembly part are mounted, and the carbon fiber plate is tensioned to the designed tension; Step 3, an anchor bolt is mounted in a hole, reserved for mounting of a steel plate, in the bottom of the girder, and the pretreated steel plate is fixed at the bottom of the girder through the anchor bolt; Step 4, the reinforcing quality of the carbon fiber plate and the steel plate is checked, the size is mainly checked, and anchoring is performed. The replaceable reinforcing design concept is adopted, secondary reinforcement is performed by replacing a reinforcing material after a reinforcing structure serves for a certain period, the carrying capacity and durability of the girder structure are effectively maintained, and the service life of the structure is prolonged.