Abstract: An analysis on the positive and negative stressed deformation of steel coil in pipe-making of spiral-welded pipe during uncoiling. The author considers that the second residual internal stress is produced due to the micro-plastic deformation of partial crystal particles in multi-crystal metal, dislocation of stressed cubic crystal of ferrite, dislocation accumulation or dispersion. The description on the mechanism of Bauschinger Effect with the second residual internal stress is made, and the influence of Bauschinger Effect on yield value of steel pipe is analyzed.