Plasma welding technique was used to weld the nickel based superalloy Inconel 625 plate (100 mm×50 mm×4 mm) with yttrium (Y) metal powder. The samples were characterized by OM, SEM and mechanical properties test. The results show that the joint formation is optimal when the welding current is 95 A, the welding speed is 110 mm/min, the plasma gas flow is 3 L/min and the content of yttrium element is 0.3wt%. The microstructure of the weld zone is fine equiaxed crystal, and the finer and more uniform grains appear in the heat affected zone after adding yttrium element. A large amount of Laves phase, carbide phase (MC) and yttrium-rich phase (Y-riched) are precipitated in welded joints. With the increase in yttrium content, the tensile strength, yield strength and elongation of the joint increase first and then decrease. When the yttrium content is 0.3wt%, the tensile strength of the sample is the highest of 776.59 MPa, the yield strength is the highest of 595.68 MPa, and the elongation is the highest of 46.60%. The overall property of the sample is higher than that without adding rare earth. Both tensile and impact fractures are ductile fractures. When the yttrium content is 0%, the hardness of weld zone is the highest, and the hardness of weld zone decreases significantly after the addition of yttrium element.