The invention relates to a welding seam microstructure refining and plasticity improving method by adding titanium-alloy powder or other material powder during titanium-alloy welding. The method includes: putting the homogeneous or heterogeneous powder into the crystallizing melting pool through a powder adding device at the end of the titanium-alloy welding melting pool; the un-melted powder is used as the core at one hand, and at the other hand, the melting of the powder is used to absorb the heat, so as to accelerate the solidification of the melting pool, thereby increasing the number of crystal grains which are crystallized simultaneously at the welding seam, ensuring the titanium-alloy welding seam microstructure refinement and achieving the purpose of improving the plasticity of the titanium-alloy welding joint.