Abstract: The microstructure and crack propagation behavior of Waspaloy alloy after service were studied by means of microstructure analysis, crack propagation rates examination, fracture morphology analysis and so on. Moreover, the microstructures of Waspaloy alloy after service were varied by the two types of heat treatment. Both the crack propagation rates of alloys after these heat treatments were measured and compared. The results indicated that there were not obvious microstructure degradations in Waspaloy alloy after service, but the crack propagation rate of Waspaloy alloy after service significantly increased; both the crack propagation rates of alloys after these heat treatments reduced.