Abstract: The flow guide tank in China advanced research reactor (CARR) acts as a reactor inlet coolant distributor and play an important role in reducing the flow induced vibration of the internal components of the reactor core. Numerical simulations of the flow field in the flow guide tank under different conceptual designing configurations are carried out using the PHOENICS3.2. It is seen that the inlet coolant is well distributed circumferentially into the flow guide tank with the inlet buffer plate and the flow distributor barrel. The maximum cross flow velocity within the flow guide tank is reduced significantly, and the reduction of flow induced vibration of reactor internals is expected.