The invention discloses a preparation method of O-ethyl-S,S-diphenyl phosphorodithioate. The preparation method comprises the following steps of: (1) adding thiophenol and sodium hydroxide into a reaction solvent, and reacting completely at the temperature of between 80 and 180 DEG C; and (2) adding ethyl dichlorophosphate into the reaction system of the step (1), reacting completely, performing post treatment, and thus obtaining the O-ethyl-S,S-diphenyl phosphorodithioate. The preparation method of the O-ethyl-S,S-diphenyl phosphorodithioate (edifenphos) has the following advantages that: 1, one-pot reaction is realized, the operation is simple, and the utilization rate of equipment is improved; and 2, active metal and sodium alcoholate are avoided, the conditions are mild, and large-scale industrialized production is easily realized.