The invention relates to the ship assembling tool technical field, and specifically relates to a round pile leg pile extension scaffold arranged in the closing portion between two pile legs; the scaffold comprises two semicircle inner clasps enclosing the outer wall of the round pile leg, wherein the two semicircle inner clasps are fixed on a tooth bar plate in the round pile leg closing portion; the scaffold also comprises an outer frame structure arranged on the two semicircle inner clasps; a steel plate is flatted on the outer frame structure, and protection rails are arranged outside the outer frame structure; the outer frame structure can be directly arranged in the closing portion in pile extension construction; the round pile leg pile extension scaffold is simple in making, low in investment, convenient in dismounting, can be repeatedly used, can prevent the conventional mode in which a steel pipe scaffold is erected from ground upward, thus reducing height, and improving safety.