Abstract: Simulated X-ray diffraction profiles are used to calculate the peak position errors and residual stress errors in X-ray residual stress measurement respectively. The dependences of the errors on half width (HW), peak intensity of line-less-background (IP) and the ratio of peak intensity of line-less-background to background intensity (IP/IB) are analyzed to deduce the errors formula for the peak position and residual stress, which are validated by the measured X-ray diffraction profiles.