Abstract: For the research reactor, introducing a neutron trap structure into the core can greatly improve the thermal neutron fluence rate peak under the condition of the core thermal power remaining the same. While the neutron trap structure introduced will have great influence on the core, it requires an in-depth analysis. Referring to the famous research reactors in the world, a new research reactor physics analysis model with a neutron trap structure was established in the paper. The relationship between the thermal neutron fluence rate peak in the neutron trap and the diameter of the Be trap was explored with the RMC code developed by our REAL Team. In the preferred size of the Be neutron trap, the thermal neutron fluence rate peak and power peak factor between the Al trap and the Be trap introduced in the established physical model were compared. The results show that the thermal neutron fluence rate peak in the research reactor with the Be neutron trap is 2.6 times in the research reactor with no neutron trap. At the same time, the power peak factor increases only 11%. This fully shows that introducing a neutron trap structure is an economical and effective way to improve the thermal neutron fluence rate peak in research reactors.