Abstract: HFETR operation experience shows that, defects exist when the nuclide trend analysis method is adopted in the analysis of fuel element damage, and the release of nuclear fuel cladding affects the accuracy of the nuclide trend analysis method. Based on the operation experiences and taking 131 I as an example, the relationship of the normal corrosion products and fission products for the HFETR sleeve-type fuel elements is analyzed, and the damage trend for the fuel element is studied. The trend K value method and radionuclide area determination method are proposed, and the accuracy of the two analytical methods is defined based on operational data, to ensure the safe operation of the reactor.