Abstract: Microstructure and phase structure of weld seam of a new type of ZA alloy for mould material,which was processed by TIG welding, were investigated by optical microscopy and transmission electron microscopy (TEM).It was shown that after the ZA alloy was processed by TIG welding,the weld seam consists mainly of columnar dendrites and a small amount of equi axial crystals; the microstructUres at room temperature are composed of η(Zn) phase,a(Al) phase, β' (ZnCu) phase and compounds of Al₄Cu₉, CuTi₂, Al₇Cu₃Mg₆.The microstructure of the weld seam is fine, some fine and thin lamellar η and α,fine dislocation and dislocation loops are found in it.After the new type of ZA alloy for mould material was processed by TIG welding,the fine microstructure of the weld seam and fine compounds in the weld seam intensify the material and improve the mechanical properties of the weld seam.