Abstract: The influence of welding parameters on filling behavor of aluminum alloy joining with pre-melting liquid filler was researched by using high-speed camera and experimental tests. The quality of welded joints was analyzed as well. The results show that two filling modes, filler wire with partial melting state and full melting state, can be founded in laser welding with pre-melting liquid filler. Liquid filler flows along the wire to molten pool when the filler metal is in partial melting state with small welding current. While in the full melting state with the large welding current, the liquid filler can flow stably into the molten pool with the help of capillary action. With the increase of welding speed, the distance between the keyhole and the weld pool edge became short. The distance between laser beam and filler should be controlled at -0.5 -2.0 mm for stable feed of liquid filler to the molten pool. The porosity rate of joints welded with pre-melting liquid filler decreased obviously compared to laser welding with no-melting filler wire.