The invention discloses a preparation method of a 
water treatment defluorination agent. The preparation method is characterized by comprising the following steps: step 1, preparing a 
sodium silicate solution, and adding a diluted 
hydrochloric acid solution for activation to obtain a solution A; step 2, weighing a first fixed amount of aluminum 
chloride hexahydrate 
solid, adding the aluminum 
chloride hexahydrate 
solid into the solution A, stirring for 10-30 minutes, continuously weighing a second fixed amount of 
ferric chloride hexahydrate 
solid, slowly adding the 
ferric chloride hexahydrate solid into the solution until the color of the solution becomes dark and turbid, continuously stirring, gradually clarifying the solution, and finally turning into a reddish brown transparent solution, so as to obtain a solution B; step 3, preparing a 
sodium carboxymethyl cellulose solution, namely a solution C; and step 4, placing the prepared solution B and the solution C in a constant-temperature water bath kettle according to the proportion, fully mixing and reacting in a high-speed stirring and heating state, and after the reaction is finished, obtaining the final defluorination agent solution. The 
fluorine removal rate of the deep defluorination agent can reach 95% or above, the 
fluorine removal rate is high, the 
fluorine removal effect is obvious, and deep fluorine removal of fluorine-containing 
wastewater can be achieved.