A Ro-ro ship route involves the USA Mobile port, which has poor water quality, more sediment and special circumstances such as sea and fresh water alternation every year, the design of ballast treatment system is more complicated than a single seawater port or a single freshwater port. In addition, the inherent operating characteristics of the Ro-ro ship will also affect the design of the ballast water treatment system. How to measure and select a suitable ballast water treatment system is the focus of this dissertation. Based on the vessel, analyzed the type choose, working principle for BWTS. It provides valuable reference for the design and construction of the BWTS for the future possible follow-up ship or similar ship.