The utility model relates to a rear-mounted triangular rocker type long-stroke oil pumping unit, which consists of a motor (1), a crank (4), a gear reducer (5), a connecting rod (7), a triangular rocker (10), an ejector rod (11), a steel cable (12), a pulley (13), a walking beam (14) and a horse head (15). One end of the connecting rod is connected with one end of the crank while the other end is connected with one end of the walking beam, the middle portion of the walking beam is mounted at the top end of a tower (6), one end of the walking beam is connected with the connecting rod while the other end is equipped with the horse head, the triangular rocker is ranged on a rear arm of the walking beam via a lower fulcrum, a middle fulcrum of the triangular rocker is connected with one end of the ejector rod, an upper fulcrum of the triangular rocker is connected with one end of the steel cable, one end of the ejector rod is mounted on the tower, and one end of the steel cable is arranged on the upper fulcrum of the triangular rocker while the other end is connected with a cable locker (17) after winding around the pulley and the horse head. The oil pumping unit realizes long stroke and has fine energy-saving effect, simple structure and high operation reliability.