The invention relates to the field of seawater desalination, and concretely relates to a modular portable reverse osmosis seawater desalination integration apparatus and a use method thereof. The apparatus is characterized in that a water intake pump, a bactericide dosing device, a filter, an ultrafiltration membrane assembly, a circulating pump, a reducing agent dosing device, a scale inhibitor dosing device, a high pressure pump, a reverse osmosis membrane assembly, a post-treatment dosing system, a cleaning water tank and a foldable water storage bag form a reverse osmosis seawater desalination system, the above devices except the water intake pump, the cleaning water tank and the foldable water storage bag all are fixedly installed in a trailer box body, and the whole body is a reverse osmosis desalination module. A pretreatment unit, a reverse osmosis desalination unit, a chemical dosing unit, a chemical cleaning unit and an electric and control unit are compactly, stably and reasonably integrated in the trailer with a closed box body trough a filter + ultrafiltration + reverse osmosis double membrane process, so the apparatus has the advantages of small size, light weight, flexible movement, and realization of transportation through aviation, highway, railways and ships.