Abstract: Analyzed here in the essay are the physiochemical properties,the macrostructure,the metallographic structure of the crack and the fracture morphology of the S135 drill pipe joint in order to find out the causes for the washout failure of the hardbanding area thereof.As a result,it is identified that the root cause for the early-happened washout is that when welding the hardbanding with the build-up process,owing to some improper heat treatment method as employed,circumferential cracks occur on the hardbanding,and part of the cracks has even extended into the joint body.Moreover when the anti-slips-collapse drill pipe is passing by the kick-off point of the shallow directional well,due to its large wall thickness,the bending stress as produced by the outer wall of the joint is rather large,which makes the existing cracks rapidly extending.