The invention provides a method and die for manufacturing a steel inner-cooling piston. The die mainly comprises an upper die, a middle die, core pulling mechanisms and a lower die. The upper die comprises an upper die body, an upper die top plate, a skirt cavity core, a cleaning push plate, cleaning rods and oblique guide columns. A circular concave pit used for containing the cleaning push plate is formed in the center of the upper die top plate. An exhaust channel is formed in the lower plane making contact with the upper die body. The middle die comprises a middle die body and a middle die sleeve. The middle die body is composed of a left half die body and a right half die body which are parted vertically, and the middle die body is used for forming the shape of the piston. Each core pulling mechanism comprises core pulling oil cylinders, pin hole cores and mounting structures. The lower die comprises a material cavity, a lower die plate, a supporting plate, a horizontal sliding way and pressing heads. According to the method for manufacturing a steel inner-cooling piston blank in the embodiment, a core identical with an inner-cooling cavity in shape is used for forming the inner-cooling cavity, a liquid die forging technology is adopted for blank forming, the material utilization rate and manufacturing efficiency can be effectively increased, and the structure performance can be ensured.