The invention discloses a method for preparing carbide derived carbon by a fused salt electrolysis method. The method mainly comprises the steps that metal carbide serves as a raw material, and is subjected to die pressing sintering to form a metal carbide sheet to serve as an anode; by taking fused salt as an electrolyte, and a high-purity and high-density graphite rod as a cathode, fused salt electrolysis is performed in an electrolysis furnace in an argon atmosphere with the electrolysis temperature of 400-1300 DEG C, the electrolysis voltage of 1.8-3.2V, and the electrolysis time of 2-60h; after the electrolysis, an anode product is taken out, and subjected to water washing, ultrasonic-assisted pickling, water washing and drying treatment; and the carbide derived carbon is prepared. According to the method, the low-cost metal carbide can serve as the raw material for preparing the carbide derived carbon by the fused salt electrolysis method, so that a preparation technology is simplified; the cost is lowered; and the prepared carbide derived carbon serves as an electrode material of a supercapacitor, and has high specific capacity and good cycling stability.