To establish a method for predicting the delamination life under thermal gradient mechanical fatigue (TGMF) conditions considering thermally grown oxides and sintering behavior, degradation tests were conducted on a thermal barrier coating (TBC) under various degradation conditions. Accordingly, damage factors were defined, and a life prediction method was developed by applying them to the constant term of the strain–life diagram. For validation, a TGMF test was performed on a specimen in which the same TBC was applied to a different type of substrate (CM247LC). The actual and predicted lives were similar, thus confirming the validity of the prediction method.