A fully-automatic cutting and welding apparatus for stepped steel plate, comprising a multi-function motion module (1), an automatic feed library turntable (2), a product flip platform (3), a steel plate bearing module (4), a pedestal (5), and a base (6). The multi-function motion module (1) is capable of performing motion in a Y-axis direction on the pedestal (5); the pedestal (5) is fixed on a surface edge of the base (6);the automatic feed library turntable (2) is fixed at one end of the base (6); the product flip platform (3) is disposed between the automatic feed library turntable (2) and the steel plate bearing module (4), and the steel plate bearing module (4) is fixed at the other end of the base (6) for bearing and fixing a steel plate, and is used as a welding platform for the final steel plate step part.