Abstract: This paper reported a study on the stress relaxation behavior of polyethylene (PE) pipe-welded joint under the mechanical load condition by an experimental method. A crack defect model was established for PE pipe-welded joint by a combination of the finite element analysis software Abaqus, and the stress intensity factor for the PE pipe with crack defects was calculated by importing the Prony series of PE pipe-welded joint and pipe-grade PE resin. This article provides a proper fracture criterion for PE materials to determine their critical stress intensity factor and stress intensity factor so that a safety assessment could be well conducted for defective PE pipes.