The invention discloses a steel piston. A piston body is internally provided with a combustion chamber bottom structure integrally connected with a piston barrel, moreover, the center part of the combustion chamber bottom protrudes towards a combustion chamber, a combustion chamber cover plate is designed to be of an annular structure, the inner ring of the combustion chamber cover plate and the outer ring of the piston body are assembled and connected in a threaded connection mode, an annular cooling oil cavity is formed, and the bottom of the cooling oil cavity is provided with an oil feeding and discharging port; and the outer side of a matching part between the combustion chamber cover plate and the piston body is provided with a sealed welded seam so that the integrated steel piston provided with an inner cooling oil cavity can be formed. The steel piston provided by the invention is simple in structure, easy to machine and low in manufacturing cost, the cooling oil cavity is easyto form, force borne by the combustion chamber cover plate is small, and the inner and outer threaded connection mode is enough to ensure the effect that the combustion chamber cover plate is not prone to be disengaged abnormally in the piston working process. The steel piston can meet the requirements that an engine is high in power and strength and low in emission amount. The invention furtherdiscloses a manufacturing method of the steel piston.