Abstract: ER2209 duplex stainless steel thin-walled specimen was fabricated by plasma arc welding on the surface of Q235 substrate. The microstructure and mechanical properties of the thin-walled specimen at different layers were analyzed.The results show the microstructure of the thin-walled specimen is composed of ferrite matrix and various forms of austenite,including grain boundary austenite, Widmanstätten austenite and partially transformed austenite, and no other harmful phases are found. The austenite content increases from 42% of the fifth layer to 58.5% of the 30 th layer. The ultimate tensile strength decreases from 887 MPa of the fifth layer to 720 MPa of the 30 th layer, while the elongation increases from 32.9% of the fifth layer to 40.7% of the 30 th layer. The fracture mechanism of the specimens at different layers is ductile fracture.