Abstract: The mechanical properties such as tensile strength ,yielding strength ,elongation rate,percentage reduction of area and hardness were tested under normal temperature condition for 20G steel which was commonly used in Xinjiang heavy oil field heat steam injection pipeline after running for almost five years,the mechanical properties of different part of the pipeline were gained. The relations between pipe’s microstructure change and properties degradation were discussed through metallography observation and mechanical properties experiments,and mechanical properties degradation situations of different parts of the pipeline were obtained. The influencing factors of the mechanical properties degradation were analyzed. The protective measures against potential safety problems caused by performance degradation of the pipeline were also proposed.