The invention provides a fishtail rudder comprising a front end, a middle body and a fishtail, wherein the front end comprises a rudder head tube which is smoothly transited to and connected to the middle body; the middle body is a streamlined NACA airfoil with rudder side plates on both sides; and the fishtail comprises a trailing edge plate connected with the middle body, wedge-shpaed plates onboth sides of the fishtail and a plane tail transom plate at the rear part of the fishtail. The fishtail rudder also comprises a plurality of vertical partition plates and horizontal partition platesfor reinforcement. A corresponding horizontal partition plate is arranged between every two vertical partition plates and a corresponding water flow hole is arranged on each horizontal partition plate. The fishtail rudder is divided into several parts by the vertical partition plates and is bilaterally symmetrical.