Abstract: Aiming at the problem that the equipment that meets the requirements of ISO 10113:1991 and ASTM E517 for automatic measurement of the plastic strain ratio (r value) no longer meets the requirements of ISO 10113:2020 standard, the measurement uncertainty of the calculated r value of ISO 10113:2020 and the measurement uncertainty of the calculated r value of ISO 10113:1991 are analyzed according to the formula of the combined standard uncertainty. The results show that the combined standard uncertainty of calculated r value in ISO 10113:2020 is greater than that in the ISO 10113:1991; the revision of GB/T 5027—2016 should meet the requirements of ISO 10113:2020 and ASTM E517.