The invention discloses self-propagating brazing heat source medicinal powder, a self-propagating brazing device and a preparation method thereof. 20 to 45 mass percent of Fe2O3 powder, 10 to 30 mass percent of Al powder and 30 to 50 mass percent of CuO powder are uniformly ground to obtain heat source medicinal powder; the heat source medicinal powder is filled into a heat temperature-resistant container of which a bottom part is provided with a through hole, a brazing heat-conducting tank of which a bottom part is open is put into the heat temperature-resistant tank to squeeze the heat source medicinal powder between two containers, a brazing filler metal is positioned in the brazing heat-conducting tank, and a lead is inserted into the heat source medicinal powder. During the welding, the self-propagating brazing heat source medicinal powder is put at a to-be-welded position of a workpiece, the lead is ignited, welding powder performs thermit reaction and discharges heat to melt the brazing filler metal, and the brazing filler metal is dropped at the to-be-welded position to form a welding seam. In the invention, the welding powder is utilized to perform the thermit reaction and discharge heat to melt the brazing filler metal so as to realize welding without any welding equipment or a power supply, the welding operation is simple, convenient, rapid and safe, a thermit reaction product can be well separated from the brazing filler metal, the welding seam is relatively pure, the heat input is low, the thermal deformation of a parent metal is low, and controllability is high.