Abstract: On the basis of the fuel particles cracking model of bubble size homogeneity,the cracking model with bubble size heterogeneity was proposed according to stress equilibrium condition that the equivalent effective stresses applied by the gas bubble are identical.The effect of the fission gas bubble size on the internal characteristics,such as equivalent fuel thickness,gas atom number,bubble pressure and maximal tensile stress,was analyzed through this proposed model.The results show that the equivalent thickness is linearly dependent with the bubble radius when the bubble radius is larger,while the ration of equivalent thickness to bubble radius increases rapidly with bubble radius decreasing when bubble radius is smaller.The gas atom concentration increases as the bubble radius decreases.The increasing rate of maximal tensile stress at bubble wall is larger than that of cracking resistance during heating process,and the cracking temperature of fuel particle decreases with bubble radius.