Taking an ultra deep water well completion and workover ship as the research object， a method of its operation probability around main offshore oil and gas regions is studied based on hydrodynamic analysis in frequency and coupled analysis in time domain. The sea state in several offshore regions is studied and analyzed based on rules and codes recommendations. The analysis results show that the ultradeep water well completion workover ship can meet the operation requirements in mild sea areas， and has a relative high probability of operation in the sea areas of southern South China Sea， West Africa and Brazil. Its operation ability in severe sea areas should be studied based on detail technical analysis and metocean data， to ensure a sufficient operation weather window for well completion and workover operation. The analysis method in this paper can be used to evaluate the operation capacity of the same type and other offshore engineering vessels.