During laser cladding, welding, and other hot forming processes, dissimilar metals can form segregation bands. These bands often lead to solidification cracks that can directly affect the mechanical properties of the processed and formed materials. To study the formation mechanism and evolution of segregation bands during metallurgical bonding of dissimilar metal materials, a two-dimensional melting and solidification model for laser cladding of IN718 on 316L stainless steel was used. This model was established using the cellular automata method and Eulerian multiphase flow algorithm. The evolution of the temperature field, molten pool morphology, melt flow, and element distributions during laser cladding was comprehensively analyzed. The rationality of the model was confirmed by comparing the melt pool geometry and grain orientation. Additionally, the reliability of the model was confirmed by comparing the distribution of Fe element content in the x- and y-directions. The simulation results reveal that during the metallurgical bonding process of laser cladding IN718 alloy on the 316L stainless steel substrate, distinct segregation zones are observed, which are characterized by the enrichment of Fe and Ni elements and an unideal alternating distribution pattern. This finding is in high consistency with the experimental results. The Marangoni force drives more Fe elements from the bottom of the melt pool (substrate) to the rear end of the melt pool, increasing the temperature of the liquidus at that location. This solidification promotion at the rear end of the melt pool causes actual solidification liquidus temperature(T_a) to be biased toward substrate liquidus temperature(T_b), resulting in the formation of a region with a high concentration of Fe elements. The rear end of the melt pool takes on a “bulging” shape, increasing the melt flow rate within the pool. This increase rolls more Fe elements from the front end of the melt pool (powder) to the rear end of the pool. Consequently, the liquidus temperature at the rear end of the melt pool decreases, biasing T_a toward the liquidus temperature of the powder(T_p). This process hinders solidification at the rear end of the melt pool, resulting in the formation of a region with a reduced concentration of Fe elements. The rear end of the melt pool flattens gradually, decreasing the melt flow rate and drawing more elements from the front to the rear end. This change results in the formation of a segregation zone with an alternating distribution of high and low Fe element content, which is consistent with the experimental results. Through the analysis of the distribution of Fe elements in the melt pool, the morphology of the melt pool and the evolution of the melt flow state, it is evident that this segregation zone arises from the mismatch between fluid flow dynamics and the morphological changes of the melt pool during the solidification process. The rate at which the solid-liquid interface moves can be calculated by finding the difference in the solute concentration between the interface neighboring cells. Fluctuations in the molten pool flow cause the morphology of the rear end of the molten pool to constantly change, resulting in varying concentrations of Fe element after solidification. Therefore, increasing the homogeneity of element mixing in the molten pool can reduce the degree of segregation. During the experimental process, appropriate increase in the laser power and scanning rate reduction can improve the quality of the cladding layer.