Abstract: The plastic strain ratio r value of metal materials was measured and calculated by using single pont method and linear regression method. The results show that the r value is calculated under low strain can not truly reflect the mechanical properties of samples. For uniform plastic strain materials, the r value can be calculated accurately by using single point method and linear regression method. Whether the straight line obtained after linear regression is forced to pass through the coordinate origin or not the difference of results is not obvious.The parallel section length should not be close to the gauge distance to avoid the non-uniform plastic strain during r value measurement.