Abstract: Based on the welding fabrication of heavy cast steel components for offshore equipment, welding procedure qualification test is conducted on dissimilar weld joint between casting NORSOK M-122 Gr420E with thickness 150mm and low alloy steel F36 with thickness 75mm. This study details the welding process, welding consumable selection, groove design, optimization of welding parameters, mechanical property test, and critical point of welding quality control. The results of process test and construction production show that welded joints meeting construction requirements can be obtained through adequate preheating before welding, strict control of interpass temperature and welding heat input.