The invention relates to a powder filling plasma arc welding method for a titanium alloy plate and a stainless steel plate, and belongs to the technical field of welding. The method is characterized in that a powdery Ni-Cu-Nb-Y2O3 composite powder filled the portion between the TC4 titanium alloy plate and the 304 stainless steel plate to serve as a middle layer material, and a plasma arc is adopted as a heat source; Ni and Cu are used to form a solid solution phase in a weld joint so as to inhibit a brittle intermetallic compound generated by direct reaction between Ti and Fe, the copper element is added to reduce the melting point, the Nb element and the Y2O3 rare earth oxide are added to improve the fluidity of the weld joint and the wettability of the base material; the stainless steelbase material is partially melted by controlling the plasma arc welding process, the titanium alloy is micro-molten, and then reliable welding of the titanium alloy and the stainless steel is realized. The method has the advantages of being simple in process, adjustable in weld joint composition, good in forming and the like, and the obtained weld joint is free of cracks and air hole defects andis reliable in connection.