The rotors of steam turbine in ultra supercritical units suffer more fatigue cycle times during operation than the required value in conventional design specification.So the design and analysis for the component fatigue life based on the conventional design specification has high risks when the fatigue cycle time the rotor suffered is higher than 108 cycles.Thus

the high-cycle fatigue experiments were carried out for25Cr2 MoVA steel

which complies with the rotors' manufacture technical specifications.Moreover

the P-SN curves were fitted based on the unlimited fatigue's semi-logarithmic model

the limited fatigue's semi-logarithmic model and the limited fatigue's semi-logarithmic bilinear model

and the fatigue fracture was analyzed.The results show that

the conditioned fatigue limits under the 108 times of cycles was 465 MPa.The analysis of the operational safety and reliability for the ultra supercritical units' rotor meet the practical requirements when the P-S-N curve was fitted based on the unlimited fatigue's semi-logarithmic model.The crack initiation came from the material surface and crack propagated radically and it was the short life stage of the P-S-N curve at high stress.