Abstract: For the same batch of Gr.2 heat transfer tubes, the tensile properties fluctuate greatly, and there is an unqualified phenomenon. Therefore, the chemical composition, mechanical properties, metallographic structure and fracture surface of heat transfer tubes were analyzed to determine the cause of the fluctuation of tensile mechanical properties. The results show that, the oxygen content of the Gr.2 heat transfer tube is low, which makes the annealing temperature range narrow. Meanwhile, the annealing temperature is chosen near the starting recrystallization temperature, and the vacuum annealing equipment has a temperature control deviation of 10-20 ℃, so it forms various degrees of recrystallization microstructure, which can lead to significant fluctuation of tensile mechanical properties.