The invention discloses a surface mechanical attrition treatment and ultrasonic wave collaborative assistance dissimilar metal TIG melting and brazing method. The method includes the step B that TIG melting and brazing is achieved through assistance of ultrasonic waves in the welding process. The method is characterized by further including the step A that surface mechanical attrition treatment is performed on low-melting-point parent metal. The method has the advantages that operation is easy to perform, the welding quality can be improved, it is prevented that welded joint structures are thick and large, brittle intermetallic compounds are prevented from being generated, the welding performance is improved, and the method is particularly applicable to connection of dissimilar metal under the condition that metal oxide can be easily generated on the surface of the low-melting-point parent metal in two types of parent metal.