Beryllium is a light rare metal, which is broadly used in nuclear energy, aviation and aerospace industry. As a structural material, the residual stresses in it during processing have a harmful influence upon its products in use. So it is very important to measure the residual stresses. Overcome the shortcoming of traditional X ray residual stress measuring techniques, X ray computer tomography is presented. This technique used in the present analyzer can non-destructively measure light metals' residual stresses with depth resolution, such as beryllium, by altering measuring and evaluating method. The residual stresses at the surface nearby welding of arc Beryllium weldment , the depth of 0.5 mm and 1.0 mm under the surface are evaluating by X ray computer tomography, meanwhile the stress free lattice spacing, d 0 , of beryllium (103) plane is calculated with this technique. The result shows that d 0 is closed to the one calculated by the lattice spacing formula of crystallograqhy.