During the drilling operation,the drill pipe near the surface usually stands the largest tension and torsion.Stress concentration is relatively serious in the upset transitional section of the drill pipe,where initiation of fatigue cracks,washouts and even fracture accidents are prone to happening.Based on the actual operating loads of G105 drill pipe,which is near the well head of an ultra-deep vertical well,finite element model of the inner upset transitional section containing a circumferential semielliptical surface crack was established.The fracture characters of the cracked model were simulated under the combination of tension and torsion.For different loading ratios and crack depths,the transition aspect ratios are determined and variation laws of the dimensionless stress intensity factor are fitted along with the crack propagating.This paper provides a basis for study on the fatigue life of drill pipe which is subjected to combined loads.