Abstract: The variation regularities of the dimensions and the mechanical properties of the HSAW pipe under different expansion rate conditions are researched by means of the expansion experiment to the pipe body. It is revealed via the experiment that the expansion process obviously improves the geometric dimensions of the HSAW pipe body,whereas has no obvious effect on the impact performance of the pipe body;the transversal tensile yield strength of the pipe body as a whole shows a rising trend,and in case of expansion ratio of 0.7%,and after the expansion,the yiel strength of the base metal rises approximately up to 30 MPa. And long with the increase of the expansion ratio,the yield strength is getting increased.Compared with the change of the yield strength,the change of the tensile strength is further more insignificant,which leads to the rise of the yield ratio as a whole,and most of the values excess the applicable standard-specified requirements. Accordingly it is suggested that for the expansion process,provided that the requirements for the pipe geometric dimension accuracy and the mechanical properties are met,a rather small expansion ratio be used as far as possible so as to prevent the negative effect by excessive big expansion ratio.