Abstract: Laser welding with pre-melting liquid filler was developed to suppress the energy reflectivity of laser by filler wire and fluctuation of keyhole during welding process. The liquid filler was pre-melted by arc and then flowed into molten pool. The melting and transfer mode of laser welding with pre-melting liquid filler and the melting and filling characteristics under different process parameters was investigated. The results show that two kinds of transition modes occurred, i.e. liquid bridge transfer and droplet transfer. During laser welding, the upper filler wire was melted and the bottom part remained unchanged at small welding current. On the contrary, droplets formed at the filler wire tip at large welding current, the transfer stability became worse. To improve the stability of droplet transfer, the liquid filler could flow into the molten pool with the help of capillary. The stability of keyhole was improved because the impact of liquid filler on the keyhole was suppressed during laser welding with pre-melting filler wire.