An　investigation　was　carried　out　on　the　behavior　of　concrete　under　both　sulfate　attack　and　mechanical　stress.　The　flexural　strength　of　the　concrete　was　determined　every　month.　Results　release　that　the　presence　of　stress　obviously　accelerates　the　sulfate　attack.　In　the　early　time　stress　accelerates　the　increase　of　flexural　strength,　but　in　the　later　time,　the　decrease　of　flexural　strength　is　also　more　obvious　than　the　concrete　subjected　to　sulfate　only.　The　effects　of　different　mechanical　stress　are　slightly　different,　the　higher　the　stress　level　is,　the　more　slowly　flexural　strength　increases　and　decrease.