Abstract: P92 steel is often used for the high temperature and high pressure components of boiler, the performance of the welded joint is vital for the safe running of the unit. Therefore, this paper conducted the low cycle fatigue test of P92 steel weld metal under 630 °C, and studied the low cycle fatigue behavior and the relationship between cycle stress and strain. Moreover, an approach of plastic strain energy density is used for predicting the low cycle fatigue life. At the same time, the mechanism of fatigue fracture for P92 steel weld metal was studied by the fracture morphology analysis. The results indicated that P92 steel weld metal performed a behavior of cyclic softening, its fatigue life and strain amplitude are satisfied with the Coffin-Manson relationship, and the way of plastic strain energy density is applied well to P92 steel weld metal. The reason for the decrease of fatigue life at high strain amplitude is the increase of the density of secondary cracks.