Abstract: Under high burnup conditions, the thermal conductivity of fuel pellet degrades, which is referred to as thermal conductivity degradation (TCD). TCD phenomenon influences fuel average temperature and fuel storage energy under steady state condition before loss of coolant accident (LOCA) and further influences peak cladding temperature (PCT) during large break LOCA process. In this study, the sensitivity analysis on double ended guillotine break of cold leg in CAP1000 at different burnup conditions was performed by using large break LOCA analysis code WCOBRA/TRAC, and PCTs under different conditions were obtained. The modified NFI (Nuclear Fuels Institute) TCD model was adopted to model fuel thermal conductivity after degradation in analysis and the decreases of peaking factors including F_Q and F_Δh after 30 GW•d/tU were also considered. The sensitivity analyses show that after considering the influences of TCD and peaking factor decreases, the PCT limiting case does not occur in low burnup range again, but occurs at burnup about 29 GW•d/tU. Compared to other burnups, the first and second peak values of PCT at that burnup point are all at the highest levels. Performing of this study can provide reference for analysis and estimation of large break LOCA of passive nuclear power plants under high burnup conditions.