Based on the theory of contact non-linear finite element, the non-linear finite element analysis model of drill pipe joint screw was established, and the effect regular of external diameter of drill pipe joint on the its strength was researched by means of large general-purpose finite element analysis software .The result indicates that the ways of properly increasing the screw diameter can effective improve the stress distribution of the inner of joint screw, also the joint screw strength of drill pipe was increase 32%.