Abstract: A workpiece was formed by bending a 6 mm thick 700L steel plate. After forming, a long crack appeared near the bending edge and broke. The cracking reasons of the workpiece were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, scanning electron microscope and energy spectrum analysis, metallographic examination. The results show that there were surface cracks in the steel plate, which led to the cracking of the steel plate after bending. The cause of the surface crack was that there were cracks on the surface of the original billet, and the cracks were flattened and extended during the later hot rolling process.