To solve the traffic efficiency problem of ro-ro ships in Hainan Xiuying Port so as to improve the traffic capacity and safety level, we propose a mathematic model based on vessel characteristics, manoeuvring features and boundary conditions of the waterway in that area according to relative regulations of Design Code of General Layout for Sea Port. Based on the theoretical calculation, waterway traffic simulation and full scale trial, we study the two-way traffic capacity of Xiuying channel and know that Xiuying port can satisfy the demands of existed ro-ro ships , and put forward some suggestions concerning the safety measures.