To study the high stress volume effect on the low cycle fatigue damage of disk, and improve the precision in the life of disk, considering the deficiency of precision in forecasting the medium and long life of disks by the volume method based on the strain life a volume method based on the SWT model for analysis of the probability life of disk was proposed. The method is based on the SWT model which regards the maximum principal strain plane as critical plane, combining with the volume method in which the size effect were considered, and it is unnecessary to consider the correction of mean stress. Then the fatigue probability life of a fan disk was analyzed using the method given. The computational median life fits well with the experimental one, precision of forecasting is higher than the result by the point method based on the strain life and the method of stress correction coefficient. It is shown that volume method based on the SWT model can be used to estimate the medium and long probability life of aero-engine fan disks.