Abstract: Based on how to calculate tensile strain hardening exponent n value with a serrated yield effect curve prescribed in ISO 10275:2007 and GB/T 5028-2008,three test methods were used including the international linear regression test for nline, the linear regression test for ntest and the difference average test for nsingle with Zwick testing machine, and a comparison of three test methods was maken to with a serrated yield effect curve and without a serrated yield effect curve. The results showed that the international linear regression test for nline, the linear regression test for ntest and the difference average test for nsingle with Zwick testing machine can be used at the same time to without a serrated yield effect curve. While to with a serrated yield effect curve, the difference average test for nsingle can not be used, the methods to test nlineand ntest can be used. Meanwhile nline and ntest were tested with a serrated yield effect curve, the regression interval should not be too small.