Abstract: How to cool down the reactor core after it is shutdown is one of the most important safety problems for China Advanced Research Reactor (CARR). The cooling measure will have a great effect on it’s investment of construction. The forced circulation and the natural circulation are two ways used at shutdown mode. The forced circulation includes two parts, one is the running inertia cooling of the main coolant pump, the other is emergent cooling core system. At the last state of forced cooling, the natural circulation valve will automatically open and coolant will be reversed, then the forced circulation turn into natural circulation. This strategy will widen the method and accumulate the experiences for domestic research reactor and also testify that CARR is safe, economical and advanced.