Abstract: The influence of the inclusion formed in solidification process on the microstructure and mechanical properties of BAg40CuZn(Mn, Ni, Co) Ag-based filler metal was investigated. When the filler metal was melted under air condition, some inclusions (Mn₂O₃, Co₃O₄, MnN) were formed owing to the reaction between element Mn and Co with oxygen and nitrogen in air. The plastic deformation ability of the BAg40CuZn filler metal was decreased because of the higher hardness and lower deformability of inclusions. At the earlier stage of the deformation, the extrusion force is sufficient to break the inclusion in matrix. The broken inclusions distributed along the direction of extruding. At the later stage of deformation, the extrusion force was decreased that is not sufficient to break the small inclusions. These inclusions decreased the stress bearing area of the filler metal, resulting in stress concentration nearby. When the stress is greater than the yield limit of the matrix, crack would initiate around the inclusion. With the increase of stress, the crack propagates that causes the damage of filler metal finally.