Abstract: During the following drawing process,the harding linear steel 70 ( 8.00 mm) appeared transverse bamboo knobs shape crack.Through chemical composition analysis,microstructure and nonmetalic inclusion exammation,and micro-hardness testing,the results showed that,the asymmetry of microstructure,and the hard and brittle acicular martensite,both factors introduced the inconsistent deformation in the drawing process. The inconsistent deformation caused the harding linear steel 70 ( 8.00 mm) transverse bamboo knobs cracking.