Gear box and marine propulsion system

The invention discloses a gearbox and a marine propulsion system, and belongs to the technical field of ships. The gearbox comprises a box body and a coupler, an input shaft, an intermediate transmission shaft system and an output shaft are rotationally connected to the box body, the input shaft and the output shaft are in transmission connection with the intermediate transmission shaft system, the input shaft is a hollow shaft, the coupler and the input shaft are arranged in the same center line, the coupler is connected with the input shaft, and a propeller shaft penetrates through the input shaft and the coupler. The input shaft is separated from the propeller shaft, the propeller shaft is connected with the coupler, the end, extending out of the coupler, of the propeller shaft is connected with a host, and the output shaft is connected with a motor. The operation reliability of the propeller shaft and the operation stability of the motor are improved, the structure is compact, and the occupied cabin space