Abstract: Experiment on stress rupture life of smooth and precracked superalloy specimens shows that small preexisting crack seriously reduces the stress rupture strength and life of superalloy components.SEM and metallographic analysis indicate that the crack grows along grain boundaries by cavitation. Based on micromechanical analysis of the cavity growth and coalescence with the main crack tip, creep crack growth formulas were derived by using creep J integral parameter J and COD rate parameter δ. Experimental data on GH33A superalloy have verified the above fracture mechanical analysis.