Abstract: Six TVS-2M type pilot fuel assemblies were loaded starting from the 5th fuel cycle at Tianwan NPS Unit 1, and would be under 4-year in-core fuel operation lifetime test from the 5th cycle to the 8th fuel cycle. Based on in-core thermal-hydraulic analysis, as well as the thermal-hydraulic test measurement and fuel assembly deformation inspection for the TVS-2M type pilot fuel assemblies, it is verified that the calculation mode of the thermal-hydraulic design code is reasonable and the calculation results are in good agreement with test results. The results show that the TVS-2M type fuel assembly and the AFA fuel assembly have a good compatibility during reactor operation, and the core operation reliability and safety can also be ensured during the transition fuel cycles.