Abstract: The flow field of China Advanced Research Reactor (CARR) was simulated by SIMPLE numerical method. It is full-flow channel simulation. The inlet corresponding flow velocity was obtained based on the numerical calculation of heat transfer for single-phase water in the single cooling channel of CARR, as well as temperature distribution, with increasing inlet flow rate. And the changing rule was analyzed. Finally, the influence on the thermal-hydraulic parameters caused by inlet flow rate was reduced. The narrow rectangular channel structured by plate fuel bundles was simulated by the developed program, and some reactor safety parameters needed during the thermal-hydraulic design were ascertained. The necessary thermal process state information for the reactor accident monitoring system can be deduced from these parameters. Thus, it is necessary to simulate the flow field. And it is necessary to analyze the hydraulic characteristics inside CARR, either. Then it can provide necessary data to CARR.