To search the influence of initial strain induced in production and service period on HDPE sheath, an artificial photo-aging test and a tensile test were designed. A kind of iron fixture was devised to produce initial strain on HDPE test pieces. The aging tests were conducted on test pieces with and without initial strain in artificial photo-aging test chamber. The tensile tests were undertaken on specimens cut and processed from test pieces after aging test. Comparisons and analysis were made on tensile properties of the specimens. The results show that no obvious aging phenomenon exists in the specimens, it is not appropriate to conclude that the initial strain is the main cause of sheath crack. It is suggested that the test method should be improved.