Abstract: Analyzed are the causes for failure of the N80-1 tubing as occurring during the fire-flooding process for thermal exploitation of a certain heavy oil well in Xinjiang via such methods as macrostructure testing,metallographic analysis and XRD.It is identified via the analysis that the fracture of the said tubing is a kind of over-load fracture.And the main reason for such fracture of the tubing is that it suffers from softening in high temperature service due to over-high temperature from crude oil combustion.And the high CO₂ differential pressure generated from crude oil combustion creates relatively severe CO₂ corrosion which causes pitting-corrosion of the pipe body,and reduces the pipe wall thickness.In addition,the pipe surface oxidation under high temperature during combustion process also reduces the wall thickness,which,in turn,promotes the over-load fracture of the pipe body.Finally,it is concluded that in general,the C-Mn series tubing is not suitable for fire-flooding thermal exploitation of the heavy oil well as above mentioned.Accordingly,it is suggested to use the Cr-Mo series special pipes made in quenched-tempered steel for serving heavy oil thermal exploitation.