The　repaired　16MnR　oil　tank　which　occurred　cracks　many　times　is　taken　as　the　research　object,　the　research　is　to　discovery　the　practicability　of　magnetic　memory　method　in　engineering　about　large-scale　ferromagnetic　components.　The　purse　is　studying　on　the　relations　between　residual　stress　of　stress　concentration　area　and　magnetic　memory　signal,　The　oil　tank　was　detected　at　different　times　when　before　and　after　repaired-phase　and　heat　treatment　by　the　way　of　magnetic　memory　method　and　X-ray　method,　At　first　magnetic　memory　method　was　used　to　detect　the　stress　concentration　and　then　X-ray　method　was　used　to　test　the　residual　stress　compared　to　magnetic　memory　signal.　The　result　show　that　original　residual　stress　is　about　1.0s,　and　the　main　reason　is　many　cracks　which　were　caused　by　the　eroded　environment.　The　residual　stress　is　decrease　to　0.21s　by　heat　treatment　on　whole　tank,　The　effect　of　heat　treatment　is　good.　magnetic　memory　signal　reflect　the　component＇s　status　about　stress　concentration　in　macroscopic,　The　intensity　of　magnetic　field　is　accord　to　residual　stress　in　basically,　So　magnetic　memory　method　can　be　used　in　engineering　to　detect　earlier　and　supply　evidence　for　residual　stress　detecting.