The　x-ray　diffraction　characteristics　of　different　materials　are　discussed　in　this　paper.　It　is　found　that　the　accurate　determination　of　real　stress　is　not　easy　to　obtain　when　two　diffraction　peaks　with　low　diffraction　intensity　are　shown　and　the　residual　stress　of　stainless　steel,　aluminum,　titanium　alloy　materials　etc　are　determined　by　X-ray　method.　Five　kinds　of　uniform　intensity　girders　made　from　common　carbon　steel　(Q235),　austenite　stainless　steel　(1Crl　8N19T1),　martensitic　stainless　steel(A335P92),　aluminium　alloy(LY　12)　and　titanium　alloy(TA15)　are　determined　repeatedly　using　uniform　intensity　girder　demarcation　method.　It　is　proved　by　experiment　results　that　X-ray　diffraction　peaks　at　some　angles　can＇t　well　reflect　the　real　change　of　stress