Background: The Integrated Head Package(IHP) is required to provide CRDM cooling.Purpose: In order to evaluate the CRDM ventilation system to ensure that there is adequate flow to cool the CRDMs.Methods: The CFD method is used to calculate the fluid field of CAP1000 reactor IHP airflow system.Results: This analysis demonstrates that the IHP design meets or exceeds the requirements and will therefore provide the required cooling air flow to the CRDMs.Conclusions: The results will provide the technical support for the choice and design of cooling fan.