Abstract: This paper designs a low-cost ship collision avoidance early warning system suitable for small and mediumsized ships, which is mainly composed of a laser ranging sensor and a dual-degree-of-freedom pan/tilt system controlled by a single-chip microcomputer. The distance between the ship and surrounding ships is dynamically monitored in the vertical direction, and "suspicious objects" that can interfere with the navigation of the ship are detected in real time and an alarm is sent to remind the ship’s pilot to take appropriate avoidance measures in time according to the actual situation. The successful application of the system provides a powerful technical means for small and medium-sized ships to achieve precise collision avoidance.