The cut, a main preparing means of specimen, will cause a difference in stress distribution between thick plate and the specimen, so this article focuses on the topic of evaluating impact of the cut on stress measurement results. Firstly, the real surface stress distribution of the plate and specimen were determined by X-ray diffraction (XRD) and FEM. Secondly, according to the specimen dimension and machining procedure, the influence of the cut on internal stress measurement is obtained and compared with the FEM results. The conclusions are as follows: (1) the normal stress of cut plane steeply decreases and the stress gradient descends along with distance away from the cut. The range of distance is approximately one-thickness of specimen. (2) In order to obtain stable and reliable results, the plane size of specimen is taken three times larger than the thickness. (3) The milling processing of layer removal method (LRM) can change the surface stress state of specimen, but the machining effects on residual stresses can be removed by properly choosing milling parameters.