Abstract: The surface residual stress of steel bars was measured by X-ray diffraction method. The influence of testing methods, testing equipment status, sample state etc. on the testing results was analyzed. The results show that:when the surface residual stress was measured, under the premise of stable state of the testing equipments, the testing parameters should be selected according to the material type and crystal structure, and the influence of the sample cutting and protection on the testing results should be taken into account; with regard to the materials of complex structure, the swinging angle could be increased to enhance the testing precision.