The invention provides a high-pressure water steam drafting device for PAN (polyacrylonitrile) based carbon fiber precursor. The high-pressure water steam drafting device comprises a high-pressure water steam drafting chamber and a maze sealing portion, wherein the upper side and the lower side of the maze sealing portion are openable, a maze plate in the maze sealing portion is composed of plates of several stages, each plate is provided with multi-stage notches, and the notches of the plates at the same stage are communicated to form channels capable of storing cellosilk beams. The direction of each channel is parallel to the running direction of the cellosilk beams. Compared with the prior art, the high-pressure water steam drafting device is simple in structure, easy to operate, low in cost and applicable to steam drafting of a plurality of beams of PAN precursor in the massive industrial production, each channel allows one cellosilk beam to run, tangling and mutual interference among the beams are avoided, friction of the PAN precursor is reduced, fuzziness and breakage of the precursor are reduced, and performance and quality of the PAN precursor are improved.