Abstract: When the heat exchange tubes of steam generators manufactured by different manufacturers at home and abroad were subjected to 350 ℃ hot tensile test, the double helix fracture appeared after the sample was broken. The formation reason of double helix fracture was analyzed by macro observation, mechanical property test, metallographic examination and scanning electron microscope analysis. The results show that the lamellar tearing behavior caused by temperature rise and torque during hot tensile test process were the main reason for the formation of double helix fracture.