A system and method for adjusting dipping time in a continuous steel pipe manufacturing line. The system manufactures a steel pipe of which inner and outer faces or any one face thereof is subjected to molten metal-plating from a steel sheet in a continuous manufacturing line, and includes an inner-face plating performing part for molten metal-plating by pouring molten metal to the upper side of the steel sheet corresponding to the inner face of the steel pipe, a steel pipe forming part that obtains a continuous steel pipe by continuously cold-forming the steel sheet subjected to the inner-face plating into a tubular shape and seam-welding a longitudinal end face joint portion of the steel sheet formed in the steel pipe, and an outer-face plating performing part for molten metal-plating by dipping the outer face of the steel pipe into the molten metal, in which a dipping length of the molten metal is adjusted in the inner-face plating performing part and/or the outer-face plating performing part.