Zr-4 alloys thick walled pipes are the important parts in nuclear power station fuel supply system, its processing capacity can be reduced through three points straightening after extrusion. The micro stress and strain variation during pipe elastic deformation, elastic-plastic deformation, and rebound deformation had been analyzed based on elastic-plastic theory, and built the M-?-? equation, which can express the relation between elastic-plastic bending deformation and unloading procedure. The Zr-4 alloys thick walled pipes elastic -linear hardening constitutive model had been built based on material characteristics to computer the straitening deformation and proposed a straightening stroke algorithm of Zr-4 alloys thick walled pipe. Several 5m length pipes with the maximum deformation more than 20mm, 6 detecting points had been used straightening experiment, and all of pipe’s straightness were less than 0.50mm and the straightening time reduced from 1.5h/pcs by hand-straightening to 22.5min/pcs automation, and the results indicate that the algorithm practical is good.