Abstract: The in pile behaviors of nuclear fuel rods are very complex under the reactor operation conditions, accurate and reliable fuel performance prediction is very important not only for the reactor safety calculation and fuel designing but also for the fuel performance assessment. In this simulation, the thermal effects and irradiation effects of UO2 material and zirconium cladding material were considered and gap heat transfer（gas heat conduction, radiation heat transfer and contact heat conduction） were considered. The subroutines were created to include above fuel models into the 3 D finite calculation and then preliminary established the simulation method for the nuclear fuel rods’ thermal-mechanical behavior.