As the key equipment of floating liquefied natural gas (FLNG) process, the performance of spiral wound heat exchanger (SWHE) influences operation costs and reliability of the whole system. The sea conditions destroy the falling film flow state of the refrigeration and then affect the heat transfer performance of FLNG SWHE. In order to design and optimize the SWHE, a cryogenic experimental device of FLNG process and a numerical model of falling film flow have been constructed to study the effects of sea conditions on the falling film flow and heat transfer characteristics of SWHE. The cryogenic experimental results show that the pitching conditions have larger effects on the heat transfer performance than yawing. Under the pitching angle of 7°, the natural gas temperature and gaseous refrigerant temperature increase by 3.22 °C and 7.42 °C, respectively. The flow rates of refrigerant and feed natural gas have a great impact on the heat transfer performance of SWHE under pitching and compound sloshing conditions. When the tilt angle increases to 9°, the tube structure with outer diameter D = 8 mm and pipe spacing S = 4 mm is recommended to reduce the drying area of the pipe wall surface.