The invention discloses a preparation method of a plant growth regulator N,N-diethylaminoethyl caprylate. The preparation method comprises the following steps: 1, preparing N,N-diethylaminoethyl caprylate hydrochloride by using a reaction chemical formula shown in the specification; 2, carrying out alkali neutralization and extraction to obtain N,N-diethylaminoethyl caprylate; and 3, preparing N,N-diethylaminoethyl caprylate citrate by using a solvent method or a solvent-free method. During use, the N,N-diethylaminoethyl caprylate hydrochloride and the N,N-diethylaminoethyl caprylate citrate can be used for spraying, irrigating and spraying agricultural products, commercial crops and fruits. The N, N-diethylaminoethyl caprylate salt is prepared through a reaction at a low temperature, andthe raw materials are easy to obtain and low in price, so the synthesis method is simple and safe, and the yield is high; in the salifying process, the use of a solvent is reduced, so the cost is saved; and the reaction time is short, so the efficiency is high, energy is saved, and the method is suitable for industrial production.