The invention discloses a telescopic wrench with the size capable of being fast adjusted. The telescopic wrench comprises an installation part, a handle, a first work part, second work parts, a third work part and a telescopic handle. An installation groove is formed in the installation part. The two second work parts are arranged on the inner side of the first work part. The second work parts are installed in the installation groove through second springs. The third work part is installed in the center of the installation groove through a first spring. A wrench body part is embedded in the two second work parts. The lower end of the installation part is connected with the handle. A first installation groove is formed in the handle. A sliding way is arranged on the side wall of the first installation groove. The telescopic handle is installed on the sliding way through a sliding groove. A positioning device is arranged in the telescopic handle and is installed in a positioning frame through a third spring. By means of the telescopic wrench, storage is convenient by adjusting the length of the handle of the wrench, multiple wrenches different in size are combined, and therefore the size types of tools are reduced, and the work efficiency is improved.