Abstract: The simulation method of the running-in phase of the HTR-10,the 10MW pebble-bed high-temperature gas-cooled reactor,has been demonstrated in this paper,based on the operation data of the HTR-10 and using VSOP,the HTGR physics analysis program.The major idea of the simulation includes the precise tracing on the power history and the fuel loading-unloading history of the core,the description of the spatial distribution of the compositions within the core at different moments,the determination of the detail simulation scheme on the fuel cycling,the effective control poisons added into the model according to the history of the control rod position,and the thermo-hydraulic feedback calculations based on the real inlet thermal conditions.