Abstract: The stress fatigue test and stress holding fatigue test were carried out in high temperature environment for round notch and V-notch FGH95 samples, and the fracture morphologies of fatigue samples were studied by means of ultra-depth of field microscope, scanning electron microscope and metallographic observation. The results show that the fatigue crack source is not obvious when the round notch sample is without load retention, and it is presumed that the crack initiation is inside the sample; when the load retention fatigue is carried out, the crack initiation is on the surface of the sample,and a relatively obvious crack source can be observed. For the V-notch sample, the fatigue cracks all originate on the surface of the sample, and the crack initiation zone is obviously pale. According to the fatigue fracture characteristics of different notched specimens, a unified creep viscoplastic constitutive model was used to simulate the mechanical evolution of fatigue cracks. The analysis shows that for the round notched specimens without load retention, the maximum Mises stress gradually transfers to the inner part of the specimen due to stress redistribution, under load retention, the maximum Mises stress is mainly located on the surface of the specimen, and the grain on the surface of the specimen is more prone to produce creep strain due to low constraint and large stress gradient, so that the fatigue crack originates from the surface of the specimen. For Vnotch samples, due to large concentration coefficient, the plasticity should be greatly changed, so that the fatigue cracks under both test load conditions originate from the surface of the sample, and the cracks originate from the notch root of the V-shaped sample.