The present invention provides a ship propulsion unit applied with an asymmetric duct. According to the present invention, the ship propulsion unit is applied with a duct which is a laterally asymmetric structure wherein an upper chord becomes narrow. The duct comprises a port support unit having a predetermined pitch angle. Therefore, resistance can be prevented to be generated by a flow delamination phenomenon due to an excessive angle of attack in a lower portion of the duct, thereby preventing propulsion reduction generated in an upper portion of the duct and improving propulsion performance of a ship.
