Abstract: The accident tolerant fuel consisted of UO₂ pellet mixed with propriety additive and zircaloy cladding smeared with special coating can reduce the fuel temperature and slow the zircaloy water reaction rate efficiently. In this paper, one of accident tolerant fuel design which is UO₂ pellet mixed with various weight percent SiC and M5 zircaloy cladding smeared with various thickness Si C coating is studied, the mixed UO₂ pellet–zircaloy cladding–SiC coating thermal relationship is built up and the thermal properties of mixed UO₂ pellet and Si C coating is collected. The long cycle fuel management for Qinshan II nuclear power plant unit 1 and unit 2 is selected as the background, the effect on fuel rod thermal performance and fission gas release of various weight percent SiC additive in UO₂ pellet and various thickness SiC coating on M5 zircaloy is analyzed comparatively, and the fuel rod performance under steady state and transient state is calculated in the end.