A bionic pectoral fin propelling device based on a planetary gear train, including a frame, a power source (1), a propelling part (2), left and right maneuvering parts (3), a fixed support plate (4), a movable support plate (5), a left pectoral fin (6), a right pectoral fin (7), a fish body (8), and a tail fin (9). The fixed support plate (4) and the movable support plate (5) are installed on the frame parallel to each other; the fixed support plate (4) is located in front of the movable support plate (5); and the left and right maneuvering parts (3) are located between the fixed support plate (4) and the movable support plate (5). The present invention solves the problem that the two pectoral fins are not synchronized, realizes variable speed propelling and left/right maneuvering, facilitates increasing the bearing capacity of the propelling device, and is particularly suitable in limited space applications.