This study considers the influence of welding speed on the dynamic behavior of the filler metal filling a molten pool. Results show that welding speed significantly influences the three-dimensional keyhole shape and flow behavior of the molten pool. When filler metal is used to fill a laser welding molten pool, an increased welding speed improves the stability of the keyhole. With the increase of welding speed, the fluctuations in keyhole depth and flow velocity at the bottom of the keyhole wall decrease, the driving force for opening the keyhole is enhanced, and the flow trend of the flow field near the keyhole from the keyhole wall to the molten pool is enhanced.