A water-wall-type passive containment cooling system, which has an outer pool (O/P) outside the suppression pool (S/P), is one passive safety system for the next generation reactors. It utilizes the steel containment vessel wall as a heat transfer medium between the S/P and O/P. /Is a measure to improve heat removal capability, the authors propose introduction of a baffle plate. The baffle plate can mitigate thermal stratification and enlarge the high-temperature region in the S/P. In particular, a hybrid baffle plate utilizes the structure wall by setting up local flow holes and enhances the natural circulation in the S/P through these holes. To clarify the effects of the configurations of the flow holes, thermal-hydraulic behavior has been examined. 1. The circumferential temperature difference in the outside region of the baffle plate was <2°C even though the flow hole area fraction was 10%. 2. The efficiency of the hybrid baffle plate saturated when the flow hole area fraction was >20%. 3. The maximum efficiency was obtained when the ratio of the depth between the vent tube outlet and the lower flow holes to the height between the vent tube outlet and the upper flow holes was ∼0.7.