Abstract: In order to reduce the error of predicting the service life of cable insulation materials, different fitting methods were used to process the mechanical properties data obtained by conventional thermal aging methods, to study the influence of fitting method on predicting the service life of insulating materials. The data of reserved elongation at break of insulating materials at different aging temperatures was fitted by linear fitting and polynomial fitting respectively, the failure time of insulation materials at different aging temperatures was determined by the fitting results, the life equation of insulating materials was obtained and the life of insulating materials used at 60 ℃ was extrapolated. The results showed that the failure time of insulating materials fluctuates with different fitting methods. Besides, different fitting methods caused the fluctuation of the failure time of insulating materials, and the fluctuation of the failure time led to the difference of the life curve, which significantly affected the prediction of the service life of insulating materials at 60 ℃.