The invention discloses a method for continuous casting of large rectangular billet of low-carbon hadifield steel. In the continuous casting process, the draw speed is 0.6-0.63 m/min; and the water distribution ratio of each section of a secondary cooling area is (27-29):(43-45):(27-29). According to the method, by promoting the draw speed, the temperature of a casting billet corner part in a straightening area is maintained at over 850 DEG C, a third brittle area is avoided, and the surface quality is greatly improved. A cooling process is optimized, the cooling of a foot roll area is weakened, thermal stress of a continuous casting billent crystallizer is reduced, and the problem that stress the casting billet is subject to stress concentration in the crystallizer and the stress concentration goes on developing in the front section of the secondary cooling area is solved. The method can remarkably reduce surface crack of the large rectangular billet, large-specification steel waste products with surface crack are avoided; the casting billet and steel surface quality can be improved; the surface of a produced casting billet sample is flat and free of recession according to acid pickling observation and basically free of surface longitudinal crack or star-shaped microcrack, the surface quality of rolled products is good, and rolled large-specification steel is free of reground waste products.