Abstract: The imaging mechanism and identification method of metal coils were investigated, and the corresponding relations between the characteristics of defects and the ultrasonic images of polyolefin electro-fusion joint were proposed. Furthermore,the integrated characteristics were presented using mathematic analysis,and the method and software for automatic defect recognition were designed.A large number of defect inspection, identification and dissection experiments were conducted on unknown defects,and the method of automatic defect recognition was verified to be an effective and fast method. Results show that the accuracy rate can reach 93.9% for joints with complex defects and 100% for those with single defects.