The invention provides an arc welding-brazing method for titanium-aluminum dissimilar alloy TIG (tungsten inert gas) arc preheating. A TIG preheating welding gun is introduced to common arc welding, a titanium-aluminum connector is locally preheated by heating a copper backing plate with a TIG preheating arc, V-shaped grooves with truncated edges are processed on two sides of each of a titanium alloy plate and an aluminum alloy plate, the copper backing plate is additionally padded at the butt joint of the connector, the TIG arc is used for heating the back of the copper backing plate, areas close to the titanium-aluminum connector are preheated by means of heat conduction of the copper backing plate, and uniform movement of the TIG preheating arc and a main arc is ensured during welding. The arc is used as a heating source, the requirement on cleaning the surface of a workpiece can be lowered by the aid of a cathode atomizing function of the arc, growth of intermetallic compounds of titanium-aluminum brazing interfaces can be hindered by the aid of an electromagnetic stirring function of the arc, appearance and distribution of the intermetallic compounds are improved, a high-strength titanium-aluminum welding connector can be formed, the equipment cost is low, practicability is high, and the arc welding-brazing method is convenient in popularization and application.