Abstract: By applying the theory of srtain energy density, and considering the influnce of residual stress of spiral welded pipeline heat treatment after welding, the paper derived the relation among the cracking propagation angle θ, crack angle β and spiral angle γ, and gave the cracking propagation angle θ of Ⅰ/Ⅱ type of cracks within the welded line zone of spiral welded pipe under the plane stress and plane strain. With above results, the equition of R resistance under the welding residual stress and outer loading stress is given and the crack-prevented pressure P is determined.