The　dissimilar　rotor　steel　welded　joint　(12Cr/30Cr2Ni4MoV)　with　buttering　layer　is　fabricated　by　using　the　combined　welding　technology　of　narrow-gap　tungsten　inert　gas　(NG-TIG)　and　narrow-gap　submerged　arc　welding　(NG-SAW).　The　shear　strength　of　joint　microzone　is　obtained　by　microshear　test,　and　the　ductile-brittle　transition　temperature　FATT50　of　microzones　is　obtained　by　partition　test.　The　influence　of　microstructure　on　hardness,　strength　and　toughness　of　microzones　is　investigated.　The　results　indicate　that　the　distribution　characteristics　of　hardness　and　shear　strength　in　welded　joint　are　basically　the　same.　The　mechanical　properties　of　HAZs　exhibit　gradient　distribution,　and　interface　mechanical　properties　mismatch　on　both　sides　of　the　fusion　line.　There　is　a　local　weakening　area　in　buttering　layer,　and　the　micro-hardness　value　is　227　HV,　which　is　the　weakest　area　of　the　whole　welded　joint.　From　base　metal　12Cr　to　30Cr2Ni4MoV,　the　ductile-brittle　transition　temperature　FATT50　of　joint　microzones　gradually　decreases.　At　20,　the　impact　toughness　of　30Cr2Ni4MoV　and　its　heat　affected　zone　is　excellent,　with　generation　of　cracks　at　the　interface　between　matrix　and　second　phase,　ductile　fracture　occurs　through　the　aggregation　of　micropores.　Quasi-cleavage　fracture　occurs　in　all　the　other　microrzones,　and　the　impact　toughness　of　welded　metal　is　the　weakest.　©　2021　Journal　of　Mechanical　Engineering.