Abstract: For cold formed straight seam welded steel pipe, the mechanical properties of steel plate before bending processing and the mechanical properties of steel pipe after bending processing were compared and researched by experiment. The results showed that the yield ratio of formed pipe was no less than that of original steel plate, and the values of yield strength and tensile strength both increased; the plasticity of pipe decreased greatly; the fluctuation of longitudinal impact energy of pipe did not change significantly and transverse impact energy decreased obviously. Therefore, mechanical properties of steel pipe could not be replaced by that of original steel plate.