The invention discloses a method for improving a solidifying ditch on the surface of an ultra-low carbon steel continuous casting slab. The improving method comprises the following steps of injecting molten steel in a tundish into a crystallizer, wherein the superheat degree of the molten steel is controlled in the range of 30-45 degrees centigrade; the water inlet temperature of the crystallizer is controlled in the range of 28-34 degrees centigrade, and the water inlet and outlet temperature difference of the crystallizer is controlled below 11 degrees centigrade; through the crystallizer, the molten steel is solidified to form the casting slab which is pulled out from the outlet of the crystallizer. According to the technical scheme, heat supply is increased before the molten steel is solidified, so that the hook structure is slowly solidified, and becomes short, narrow and shallow, and then the technical problem in the prior art that the hook structure of the ultra-low carbon steel continuous casting slab is relatively great can be solved, and the length, width and depth of the hook structure can be reduced.