Abstract: To investigate the interaction of heterogeneous solute in molten pool flow during the laser welding of heat-resistant steel and nickel-based alloys, a multiphase flow coupled welding model was developed, taking into account the combined influence of melt pool flow patterns and thermal property differences of dissimilar materials on elemental macro-segregation. The model's validity was confirmed through experimental comparison. The study examined the flow mixing of Fe-rich and Ni-rich molten metals and the formation process of Fe-rich segregation in the melt pool with varying welding speed. It was observed that in the upper part of the melt pool, Fe-rich molten metal from the heat-resistant steel side flowed backward under the action of recoil force and Marangoni force, encountering Ni-rich molten metal in rear part, and complex flow behaviors emerge, primarily characterized by forward flow and internal circulation within the pool.On the cross-section, Fe-rich molten metal entered the melt pool with Marangoni convection, partially forming banded segregation near the fusion line in the middle of the melt pool.Another portion mixed in the upper part of the melt pool in the form of vortices. At a welding speed of 2.0 m/min, incomplete mixing resulted in large areas of blocky and vortex segregation, with the highest Fe content reaching 80.29%. When the welding speed was reduced to 1.2 m/min, the increased heat input and slower solidification led to a reduction in the area of Fe-rich segregation with the highest Fe content decreasing to 63.85%.