Abstract: By means of metallographic examination, hardness testing and tensile test, the effect of temperature on the microstructure of heavy oil thermodynamic exploitation pipe and the relation of microstructure and mechanical properties were studied. The results showed that the pearlyte content in the pipeline edge was shorter obviously than the inner and the carbon content reduced. The pearlyte spheroidization and high temperature decarbonization were the two main reasons led to the carbon content reduce in the pipeline edge. Because the microstructure of pipeline had changed, the tensile and compressive properties of pipeline reduced, and the pipeline safety was reduced.