The invention discloses an all-steel piston which comprises an outer piston body and an inner piston body, wherein the inner piston body is sleeved by the outer piston body, that is, the inner piston body is arranged inside the outer piston body; the inner circumferential part of the outer piston body is in welded connection with the corresponding position of the outer circumferential part of the inner piston body; and a cooling cavity used for circulation of a cooling liquid is formed between the outer piston body and the inner piston body. The all-steel piston provided by the invention comprises two parts, namely the outer piston body and the inner piston body, and the outer piston body and the inner piston body are welded into a whole by adopting a welding method, so that the problem about the difficulty in machining of a complex all-steel piston structure can be effectively solved. Meanwhile, the all-steel piston can be cooled by utilizing the cooling cavity, so that the coking possibility of the cooling liquid can be effectively lowered.