The invention relates to tetrazole cyano boric acid ionic liquid and a preparation method thereof, and belongs to the fields of organic synthesis and pyrophoric liquid propellants. The tetrazole cyano boric acid ionic liquid is prepared by carrying out replacement reaction in an organic solvent by utilizing sodium tetrazole cyano borate and corresponding imidazole, pyrrolidine or pyridine halogeno salt; the tetrazole cyano boric acid ionic liquid has very high nitrogen content, positive formation enthalpy, high density, wide liquid range, lower viscosity, good heat stability and ultrashort ignition delay time, and has a potential application value in the field of the pyrophoric liquid propellants. In addition, the invention also provides the preparation method of the sodium tetrazole cyano borate. According to the preparation method, the sodium tetrazole cyano borate is prepared from sodium cyanoborohydride and 1H-tetrazole through one step under a heating condition, the step is simple, and no virulent raw materials are involved.