The invention relates to a long ruler, comprising a casing, a ruler core disk, a ruler spring, a ruler belt, a braking device, a middle dividing mounting plate and a driving device, which is characterized in that: the ruler core disk, the ruler spring and the ruler belt are arranged in the casing; the ruler core disk can rotate; the ruler belt is wound on the ruler core disk; one end of the rulerbelt extends out of the casing; the ruler spring is connected with the ruler core disk through the driving device; the braking device is arranged between the button of the casing and the ruler core disk; the casing cavity is divided into a left arranging cavity and a right arranging cavity through the middle dividing mounting plate, wherein the ruler spring is arranged in one arranging cavity andthe ruler core disk arranged in the other; one end of the driving device is connected with one end of the ruler spring and the other end is connected with the ruler core disk. The invention has the advantages of simple and reasonable structure, convenience for handheld usage, easy assembly and production, suitable for popularizing and applying in long ruler.