A positioning structure includes a locating member, a movable mechanism mounted in the locating member for the connection of a mop and movable up and down relative to the locating member, and a positioning mechanism mounted in the locating member for stopping against the positioning mechanism upon connection of a mop to the movable mechanism to support the mop stably in position for dehydration through a spining action after movement of the movable mechanism to the top side of the locating member.