The invention relates to a ship energy-saving bulbous bow. The energy-saving bulbous bow comprises a plurality of bulbous bow housings of different sizes, wherein the smallest bulbous bow housing (3) is fixedly and hermetically assembled with a hull; a bulbous bow housing storage region (1) is arranged on a deck or in a cabin of a bow part, and the rest bulbous bow housings are stored in the region; the bow part is also provided with a manipulator (4); according to the speed and the draft of the ship, the manipulator is used for grabbing the corresponding bulbous bow to assemble and replace on the outer side of the smallest bulbous bow housing (3). By considering the adaptability of the ship and the draft to the size of the ship bulbous bow, the bulbous bow is adjusted into a proper big one when the ship is sailing at high speed and deep draft and is adjusted into a proper small one when the ship is sailing at low speed and shallow draft so as to meet the different sailing requirements.