The three-dimensional transient laser welding heat-flow coupling model for the filler metal feeding process and the combined heat source model are established, in which the welding driving forces, such as recoil pressure, surface tension, thermal buoyancy and gravity, are introduced. The volume-of-fluid method is used to track the gas-liquid interfaces of keyholes, and the effect of filler metal on the three-dimensional shape of keyholes and the flow behavior of molten pools is studied. The influence mechanism of the filler metal filling on the keyhole stability is analyzed. The research results show that the filler metal filling is unfavorable to the stability of keyholes and the keyhole bottom is prone to close. In the autogenous laser welding process, a flow from inside to outside and from bottom to top appears on the keyhole walls, which is favorable to the stable opening of keyholes.