The invention provides a rotary propeller for an air power boat. The rotary propeller comprises an air propeller body (1), a propeller hub support (2), a first section axle tube (3), a rotary joint (4), a cross universal joint (5), a second section axle tube (6), a third section axle tube (7), an engine output shaft (8), a support (10) connected with the rotary joint (4), a servo motor (9) mounted on the support (10), a rotary gear (11), a transmission gear (12) in mesh connection with the rotary gear (11), and a drive gear (13) in mesh connection with the transmission gear (12). The rotary propeller has the advantages that the output torque of an engine is efficiently transmitted to the air propeller body, the servo motor controls the air propeller body to rotate in a plane, the course of the air power boat is controlled by changing the thrust direction, and propelling efficiency and mobility are improved as compared with traditional rudder control.