The invention discloses an effervescent tablet of a plant growth regulator composition and a preparation method thereof. The effervescent tablet of the plant growth regulator composition is made of the raw materials including the substances based on the parts by mass: 0.1-30 parts of diethyl aminoethyl hexanoate, 0.1-60 parts of mepiquat chloride, more than 0 part and less than or equal to 40 parts of water-blocking agent, 3-30 parts of acidic effervescence agent, 3-30 parts of alkaline effervescence agent, 1-10 parts of binding agent and 1-20 parts of glidant. The effervescent tablet can be prepared by a direct drying tabletting method or a wet granulation and secondary tabletting method, wherein the direct drying tabletting method can be used for preparing the effervescent tablet by mechanically grinding auxiliary agent, evenly mixing the auxiliary agent and two active components and directly tabletting; and the wet granulation and secondary tabletting method can be used for preparing the effervescent tablet by drying the two active components, grinding the auxiliary agent, preparing acidic and alkaline soft materials by mixing, bonding and pelleting, and finally tabletting. Thewater-blocking agent is introduced to solve the problem of moisture absorption of active ingredient solid preparation of mepiquat chloride; furthermore, the prepared mepiquat chloride composition effervescent tablet of the plant growth regulator diethyl aminoethyl hexanoate is a new formulation product having the characteristics of rapid disintegration, completely dissolving out of the active ingredient and accurate and quantitative field operation.