Abstract: Based on the burnup credit of actinides+fission products (APU-2) which are usually considered in spent fuel package, the effect of power density and operating history on k_∞ was studied. All the burnup calculations are based on the two-dimensional fuel assembly burnup program CASMO5. The results show that taking the core average power density of specified power plus a bounding margin of 0.002 3 to k_∞, and taking the operating history of specified power without shutdown during cycle and between cycles plus a bounding margin of 0.004 5 to k_∞ can meet the bounding principle of burnup credit.