In this paper,computational methods are used to optimize the design of a prompt-gamma neutron activation analysis (PGNAA) system on China Advanced Research Reactor (CARR).Approaches are adopted for obtaining accurate neutron beam parameter and saving the computing time.For the radiation shielding design,the optimizing factors include the cost,weight,volume,machining convenience and background radiation at the detector position.Low background spectrum and high sensitivity are expected.The simulation results,and experiences from inteational PGNAA community,were used in the design of the CARR PGNAA system.