Abstract: The coupling of neutronics and thermalhydraulics based on stochastic method of neutron transport is able to control the different codes and transfer data. The coupling methods of MCNP5 and CFX based on a single fuel rod channel model and a 3×3 rod bundle model were studied. Based on the research above, the coupling of MCNP5 and CFX applied to a Pebble Bed-Advanced High Temperature Reactor (PB-AHTR) was studied and validated by comparing to the results of the coupling of MCNP5 and RELAP5-3D. The results of the coupled calculations indicate that the effective multiplication factor will stay stable after several coupled iterations with some fluctuation. The research results demonstrate that the feasibility of the coupled code is approved, but the accuracy of the coupled calculation needs to be improved in the future research.