The utility model relates to a pipe elbow and especially relates to an internal and external tooth-shaped elbow comprising a first joint end, a second joint end and a bend pipe. The first joint end is provided with an internal thread; the second joint end is provided with an external thread; and the internal diameter of the first joint end is the same as the internal diameter of the second joint end. With the internal and external tooth-shaped elbow, connection between the internal thread and the external thread is achieved; the internal and external tooth-shaped elbow is simply structured with convenient operation; a reduction change of a pipe diameter is achieved; the external thread can be connected with an internal threaded pipe member or a pipe member with a large pipe diameter; and the internal thread can be connected with an external threaded pipe member or a pipe member with a small pipe diameter.