Abstract: China LEAd-based Research Reactor (CLEAR-Ⅰ) is proposed as the primary choice for Chinese Academy of Sciences (CAS) accelerator driven subcritical system (ADS) project. Fuel element is one of the key components in lead-based reactors. It is necessary to ensure the fuel pellet’s central temperature and cladding’s maximum temperature meet the requirements of the design criterion. The finite element code ANSYS was used to simulate the temperature field of active zone in normal operation and loss-of-flow accidents. The simulation results in normal operation show that the fuel pellet’s central temperature is much lower than the melting point and the cladding’s maximum temperature is below the operating temperature limit. The simulation results in loss-of-flow accidents show that the fuel pellet’s central temperature and the cladding’s maximum temperature significantly increase after the accidents. If the flow rate of coolant is 0.1 m/s, the cladding’s maximum temperature is higher than the operating temperature limit. If the scram delay time is more than 17.5 s, the cladding’s maximum temperature is higher than the accident conditions temperature limit. The above simulation and analysis results are to be the basis of safety review work.