Abstract: This article introduces the welding test research of S31603+Q420qENH application of stainless steel - weathering steel clad plates for bridges currently being developed in China, including the chemical composition, mechanical properties, hot processing performance tests, and weldability tests of the base material. The comprehensive mechanical properties, hot processing performance, and weldability of the S31603+Q420qENH steel plate are evaluated. A welding process qualification test was conducted for the application of S31603+Q420qENH clad plates in the Daduhe Grand Bridge project, which guided the production and manufacturing of the bridge and has reference significance for the application of S31603+Q420qENH composite steel plate in other projects.