Abstract: In view of the remarkable difference between ship reactor compartment (SRC) and nuclear power plant containment in space layout and structure size, the SRC pressure and temperature variations are more serious and relied on the dimension of SRC thermal-hydraulic model. Using RELAP5/MOD3.2 code, six SRC control volume models were established, including two-dimensional and three-dimensional models in space, and the variations of SRC pressure and temperature under supposed LOCA were analyzed. The characters of different models were studied and an optimized model was established. The result can be a reference in ship reactor SRC safety evaluation and thermal-hydraulics character analysis during LOCA.