It is easy for drill string to be cracked when it is subjected to complex forces. Evaluating the corrosion fatigue life of drill string according to the actual situation on site can provide a basis for the safe use of drill string. By calculating the axial force， cyclic stress and fatigue limit of the drill string in the wellbore， the fatigue evaluation methods of drill string based on fatigue coefficient， drill string tension and rotation counting are determined， and the influence of acidic fluids is considered. The results show that the increase of the bending stress and buckling will lead to the fatigue failure of the drill string when drilled with severe dogleg. The remaining service life of the drill string will be greatly reduced when the corresponding ROP is reduced and the rotating speed is increased significantly. When severe acid corrosion occurs， the remaining service life of the drill string will be rapidly reduced. The drill strings in the well section with high tension and large dogleg should be regularly shifted to ensure the safe and normal use of drilling string on site.