Abstract: A method for controlling speed of ships sailing in harbor waters based on ship drift calculation, Under Keel Clearance calculation and car-following theory is introduced to improve the navigation efficiency while ensuring the safety.The upper limit of ship speed is calculated according to ship squat and under keel clearance requirement.The Selection of navigation mode, single channel or double channel, depends on the width and lateral constraint of the waterway.The allowed lowest speed is calculated according to the drift caused by wind and current.Final range of the control speed is calculated with car-following theory under the condition that the longitudinal spacing between ships satisfies the safety requirement.