With stainless steel as research target, the molten pool shape and weld morphology during the process of single/dual beam laser welding are comparatively studied, and the relationship between both of them is established. The results indicate that the evolution processes of molten pool shape are different for single and dual beam laser welding and the molten pool size and weld morphology of dual beam laser welding are influenced by the spot spacing. As for the process of dual beam laser welding, the interaction of two keyholes is perpendicular to the connection line of the two laser beams which induces an enhanced melt flow, while as for that of single beam laser welding, the melts flow radiantly and evenly from the keyhole. The difference between melt flow patterns is the key to induce the difference in weld morphology under single/dual beam laser welding.