Based on the demand of weight reduction in the aeronautic and aerospace field, laser welding of aluminum-lithium alloys has received more and more attention from domestic scholars. The laser butt welding of 2 mm thick 2060-T8 Al-Li alloys is conducted and the micro-morphologies of weld seam is investigated. Moreover, the formation mechanism of the fine equiaxed grain zones (EQZ) at the boundary of fusion weld seam is clarified based on the molten pool flow mechanism. The analysis results show that the effects of laser heating and molten pool convection make the amounts and distributions of heterogeneous nucleation particles in different boundary regions of weld seam different, the EQZ width in the upper part is narrow and the EQZ width in the waist part is relatively large. In addition, part of the nucleation particles in the upper part and waist part of the weld boundary are brought into the molten pool along the tangent direction of the upper fusion line according to the molten pool flow mechanism, and on this basis, the grain grows to form a curved colony of equiaxed grains extended into weld seam.