The　microstructure　and　property　of　T91/10CrMo910　dissimilar　steel　welded　joints　after　one　and　two　years　service　have　been　studied　by　OM,　TEM,　EDS　and　Vickers　hardness　test　in　this　paper.　The　results　showed　that　after　one　year　service　the　microhardness　of　T91/10CrMo910　dissimilar　steel　welded　joints　increased　clearly　and　after　two　years　service　chromium　element　diffused　or　transferred　from　the　welding　line　or　T91　matrix　to　10CrMo910　matrix.　Coarse　lath　martensite　was　the　characteristic　of　the　microstructure　of　T91/10CrMo910　dissimilar　steel　welded　joints,　and　the　martensite　laths　became　fragment　after　one　and　two　years　service.　More　carbide　particles　had　been　observed　after　one　year　service　than　that　after　two　year　service,　which　had　a　good　agreement　with　the　results　of　the　micro-Vickers　hardness　test.