The invention discloses a preparation method of sodium diisobutyldithiophosphinate. The preparation method comprises the following steps of (1) preparing a Grignard reagent namely isobutylmagnesium bromide; (2) preparing tetraisobutyl dithiophosphine; and (3) under the action of a phase transfer catalyst, enabling the tetraisobutyl dithiophosphine to react with a vulcanizing agent so as to obtain the sodium diisobutyldithiophosphinate. According to the method disclosed by the invention, through the phase transfer catalyst, several kinds of reactants with different gathering shapes react, so that the problem that the reaction yield is not ideal because a solvent is used by a tetraalkyl dithiophosphine method is solved, the reaction time is short and only needs 2-4 hours, and the yield of the sodium diisobutyldithiophosphinate is high and achieves 80% or above.