Abstract: Through the containment pressure and temperature response analysis with the level of 100 MWe reactor after a postulated accident such as LOCA, the suppressant characteristics of suppression containment have been researched in this paper. Passive spraying can not effectively decrease the pressure of containment due to the excessive releasing enthalpy in the phase of blow-down, but the suppression containment system can effectively decrease the pressure during a short term of LOCA. Through the analysis of the important parameters, such as the total volume of suppression pool, the proportion of gas to water and flow area of pipelines, it can effectively restrain the pressure of containment in the phase of blow-down, these parameters will influence suppressant effect: firstly the total volume of suppression pool is the most important factor; secondly the proportion of gas to water and the total flow area of pipelines should be optimal.