There is a remarkable difference in stress distribution between a specimen and a plate removed from the specimen. The plate presents a uniform stress distribution whereas the specimen presents a non-uniform stress distribution. Firstly, the real stress distributions in plates with thickness of 30, 40 and 50 mm and then in the specimens were obtained through simulation and X-ray surface stress measurement. Secondly, in order to study the impact of specimens shapes and processing ways on the results accuracy, two irregular shapes (parallelogram and trapezoid) and two processing ways (saw and electron discharge machining (EDM)) were compared and analyzed by simulation and experiment using layer removal method, then the specimen effects on measurement results were evaluated. The results show that: 1) the non-uniform stress distribution characteristics of the specimen near the surface of the cut is significant, the range of non-uniform stress distribution is approximately one-thickness distance away from the cut, and it decreases gradually along the depth; 2) In order to ensure the stability in the results, it is suitable to take the specimen plane size 2-3 times of its thickness; 3) Conventional processing methods have little effect on experimental results and the average deviation is less than 5%.