Abstract: A three-dimensional continuous mixed-state model was established. The feature that molten pool is higher than the welding surface during laser welding was obtained by using level set method in the model, as well as the simulation of the mixed state of solid-liquid in the solid-liquid zone and the tracking the movement of the vapor-liquid interface. The results demonstrated that, the wall of the keyhole and the layer of the molten pool with asymmetry were thin on the front wall of the keyhole and was thick on the rear wall. Also, the temperature gradient was large on the front wall of the keyhole and was small on the rear wall. The metal vapor evaporating from the keyhole wall flowed to the axis of the keyhole, and then was ejected outside the keyhole. The maximum absorption of the laser intensity occurred on the bottom of the keyhole. The maximum temperature of 3 700 K on the keyhole wall was higher than the vaporization temperature over 567 K. The depth of the keyhole increased quickly during the initial stage of the formation. However, the changing rate of the keyhole depth gradually decreased with the increase of the depth of the keyhole.