The invention discloses a preparation method for propellant fuel. The preparation method comprises the following steps: uniformly mixing hydrazine or a methyl derivative thereof with a tetrahydrofuransolution of borane to perform a reaction, and after the reaction, performing rotary evaporation on the tetrahydrofuran solution to obtain a first product; adding a first solvent into the first product, then performing washing, and then performing rotary evaporation to remove the first solvent, so as to obtain a hydrazinoborane derivative. According to the method, hydroboration is carried out on ahighly-volatile hydrazine fuel and a methylated derivative of hydrazine, the obtained borohydride of the hydrazine is a colorless non-volatile liquid or a white solid, has no volatility and greatly reduces hazard of the hydrazine fuel, and is a novel aerospace propellant fuel since the ignition delay time of the hydrazine borofluoride is extremely short.