ABSTRACT An onshore receiving terminal provides precise docking information to the pilot by detecting distance, speed, and angle of docking LNGC using the laser or ultrasonic distance measuring device installed to fixed mooring facility. However, FSRU is on the status that mooring facility is moved to floating LNG terminal which is installed to the see-bed by the influence of weather conditions such as sea wind and ocean current, and therefore, it is hard to use existing distance measuring device, and a LNGC (Liquefied Natural Gas Carrier) comes alongside a FSRU (Floating Storage Regasification Unit) for off-loading. It is critical to maintain the tension of the mooring line between FSRU and LNGC, because LNG may be in danger of leakage and possible explosion during off-loading. This article aimed to develop docking aid system between two vessels fluids such as FSRU and LNGC based on docking guidance system technology of floating offshore LNG terminal, and a tightening control, monitoring system and algorithm was developed for the side-by-side mooring. In comparison with previous systems, they are expected to provide stably docking and control the tension of the mooring line between a FSRU and a LNGC.