Dissimilar welding between carbon steel and stainless steel is widely used in power plant. A lot of stress corrosion cracking (SCC) have occurred in the weld joint, which are affected greatly by residual stresses. This paper presents a study of residual stress in a dissimilar weld between 0Cr18Ni9 steel and 20 low carbon steel with Inconel 182 weld metal, by using neutron diffraction, X-ray diffraction measurement and finite-element method (FEM). The residual stresses show asymmetric distribution due to the dissimilar materials. The maximum longitudinal (1.92ReL304) and transverse stresses (1.07ReL304) are presented in the weld metal and heat effected zone of 20 carbon steel, respectively. Through the thickness of weld metal, the average longitudinal stress is around 370 MPa. The weld root has a stress concentration, and the stresses near the weld root in the 20 steel are larger than those in 0Cr18Ni9 steel, making the weld root become the most risk zone for SCC. With the increase of heat input, the residual stress and plastic deformation around the weld root increase. Hence, low heat input is recommended for the welding between 0Cr18Ni9 steel and 20 carbon steel.