The invention discloses an extraction method of a filament potting compound for a cathode. The method comprises the following steps of 1) preparing a pickling solution, 2) preparing an alkaline solution, 3) etching a molybdenum barrel filled with the potting compound in the pickling solution, 4) performing neutralizing treatment on the etched potting compound in the alkaline solution, 5) washing the potting compound with deionized water and inspecting a PH (Potential of Hydrogen) value, and 6) drying the potting compound in an oven and keeping the potting compound with a drying bottle. The method has the benefits that 1, the surface quality of the potting compound is good, the surface fineness is good and the surface is free from obvious impurities; 2, the potting compound is good in uniformity and good in internal and external consistency; 3, an extraction technology of the filament potting compound for the cathode is high in stability; and 4, a melting point of the potting compound is appropriate and a use requirement of a traveling-wave tube cathode can be met after potting and sintering. The method is applied to a certain air-borne traveling-wave tube at an X band; the on-off times of a filament assembly are greatly increased; a short or open circuit of the filament assembly is avoided; and the service life of the cathode can reach over 15000h.