The invention discloses a hair curler capable of adjusting the size of curled hair. The hair curler capable of adjusting the size of the curled hair comprises a handle and a heating rod which is coaxially arranged at the front end of the handle. The heating rod comprises a rod body, a center pole, an end cover, a threaded rod and a folding frame, wherein the rod body is composed of an upper heating annular plate and a lower heating annular plate; the center pole is located at the center of the rod body and fixedly connected with the front end face of the handle; the end cover is rotatably fixed to the front end of the rod body; the threaded rod is movably arranged at the front end of the center pole in a sleeving mode and matched with threads in an inner cavity of the end cover; the folding frame is hinged to the threaded rod and one side of the center pole. The folding frame can move backwards along with the threaded rod so that the folding length can be reduced and the folding height can be increased; compression turning points with changed heights on the folding frame are connected with the upper heating annular plate and the lower heating annular plate respectively. According to the curled hair size adjustable hair curler, the folding frame is compressed and folded to drive the upper heating annular plate and the lower heating annular plate to expand vertically so that hair wound around the upper heating annular plate and the lower heating annular plate can be shaped to form large-diameter curled hair; the curled hair size adjustable hair curler is simple in structure, convenient to operate and easy to process and produce.