The present invention relates to the technical field of steel billet shearing and conveying, and specifically discloses an automatic feeding mechanism for a shearing line, comprising a frame, wherein a feeding end of the frame is opposite to a shearing device, an adjusting component and a plurality of conveying components are also provided on the frame, the adjusting component comprising two movable parts and a plurality of adjusting parts, the two movable parts are arranged along the length direction of the frame, each adjusting part pushes the two movable parts to be relatively close to or away from each other, and each conveying component is arranged at intervals between the two movable parts along the length direction of the movable parts; the conveying component comprises a plurality of connecting parts and a plurality of rollers, the number of each connecting part is consistent with that of each roller and they are connected one by one, the rollers are rotatably matched with the connecting parts, two adjacent connecting parts are hinged, two connecting parts at both ends of the conveying component are respectively hinged to the two movable parts, and each roller is used for rolling contact with the steel billet. The feeding mechanism provided by the present invention improves the conveying accuracy of steel billets of different models and improves the quality of steel billet shearing operation.