A method for controlling energy-saving sailing of a ship, comprising: detecting a ship speed relative to the ground and a ship speed relative to water in real time during routine sailing; characterized by controlling the current opening degree of a throttle to increase the instantaneous oil supply amount of a main engine of the ship if the ship speed relative to the ground is larger than the ship speed relative to water and a difference therebetween is not less than a preset value; and controlling the current opening degree of the throttle to reduce the instantaneous oil supply amount of the main engine of the ship if the ship speed relative to the ground is smaller than the ship speed relative to water and the difference therebetween is not less than the preset value wherein if the ship speed relative to the ground is larger than the ship speed relative to water, gradually increasing the instantaneous oil supply amount of the main engine of the ship, calculating an oil consumption amount corresponding to a predetermined distance under each instantaneous oil supply amount in real time to identify the minimum instantaneous oil supply amount for the predetermined distance, and keeping sailing under the minimum instantaneous oil supply amount; if the ship speed relative to the ground is smaller than the ship speed relative to water, gradually reducing the instantaneous oil supply amount of the main engine of the ship, calculating an oil consumption amount corresponding to the predetermined distance under each instantaneous oil supply amount in real time to identify the minimum instantaneous oil supply amount for the predetermined distance, and keeping sailing under the minimum instantaneous oil supply amount; and repeating the above steps. detecting a ship speed relative to the ground and a ship speed relative to water in real time during routine sailing; characterized by controlling the current opening degree of a throttle to increase the instantaneous oil supply amount of a main engine of the ship if the ship speed relative to the ground is larger than the ship speed relative to water and a difference therebetween is not less than a preset value; and controlling the current opening degree of the throttle to reduce the instantaneous oil supply amount of the main engine of the ship if the ship speed relative to the ground is smaller than the ship speed relative to water and the difference therebetween is not less than the preset value wherein if the ship speed relative to the ground is larger than the ship speed relative to water, gradually increasing the instantaneous oil supply amount of the main engine of the ship, calculating an oil consumption amount corresponding to a predetermined distance under each instantaneous oil supply amount in real time to identify the minimum instantaneous oil supply amount for the predetermined distance, and keeping sailing under the minimum instantaneous oil supply amount; if the ship speed relative to the ground is smaller than the ship speed relative to water, gradually reducing the instantaneous oil supply amount of the main engine of the ship, calculating an oil consumption amount corresponding to the predetermined distance under each instantaneous oil supply amount in real time to identify the minimum instantaneous oil supply amount for the predetermined distance, and keeping sailing under the minimum instantaneous oil supply amount; and repeating the above steps.