The invention discloses a continuous device for gasifying unsymmetrical dimethylhydrazine waste liquid with supercritical water. The device comprises an unsymmetrical dimethylhydrazine storage tank, a mixer, a water tank, a preheating system and a reactor, wherein the outlet of the unsymmetrical dimethylhydrazine storage tank is connected with the first inlet of the mixer; the outlet of the water tank is connected with the second inlet of the mixer; the outlet of the mixer is connected with the inlet of the reactor, the water in the reactor is supercritical and the supercritical water and unsymmetrical dimethylhydrazine are reacted in the reactor for recycling. Compared to a kettle-type reactor, by the continuous device for gasifying unsymmetrical dimethylhydrazine waste liquid with supercritical water, the temperature of the reaction materials can be rapidly raised to a predetermined temperature, the carbon gasification rate and COD removal rate are further increased and the concentration of ammonia nitrogen in produced liquid is reduced.