Abstract: In order to study the complex thermo-mechanical behavior of the composite plate in the welding process, a finite element model was developed to simulate the welding process of 304/Q345R composite plate. The thermal cycle curve and residual stress distribution of the welded joint were obtained by thermocouple and blind hole method. The finite element model was verified by the experimental results. Meanwhile, the microstructure, grain morphology and element distribution of the welded joint were analyzed by means of optical microscope and scanning electron microscope, and the microstructure evolution of the welded joint was investigated. The results showed that the maximum welding residual stress was 312 MPa, which was located at the weld toe, and the residual stress gradually decreased and stabilized along the direction from the weld to the base metal. At the interface of the two materials, the residual stress discontinuity was observed. The microstructure of the welded joint was composed of austenite and ferrite. The ferrite in the vicinity of the fusion line of the composite layer presents strip and needle-like shape and forms a banded transition zone, while the austenite grains in the vicinity of the fusion line presents columnar morphology and smaller size.