Abstract: The working condition of drillpipe is very serious, especially in the dogleg or build section. Large alterative bending stress gives rise to the fatigue failure of drillpipe. Calculation of the fatigue life of the drillpipe can give some guidance for the use and precaution of drillpipe failure. As a result,in this paper, the three - axis stress has been analyzed based on the mechanism of fatigue failure of drillpipe, and a model for the calculation of fatigue life of drillpipe is proposed, which can be used for the prediction of fatigue life of crackled or noncrackled drillpipe. Results of example show that the model is reasonable and coincident with the field data.