The invention discloses a preparation method of dimethyldiallylammonium 
chloride, which comprises the following steps: in a continuous pipeline type reactor, keeping the temperature at 15-35 DEG C, reacting a 
dimethylamine water solution having a flow rate of u kg / h and chloropropene having a flow rate of 1.27-1.54u / n kg / h until the free amine concentration is lower than 3.8*10<-4> mol / g, wherein the pH value is controlled at 7.0-12.0 in the reaction process; then, regulating the 
reaction temperature to 35-60 DEG C, controlling the pH value of the reaction solution at 8.5-12.0, and further reacting until the free amine concentration is 5.1*10<-5> mol / g; and after the reaction is finished, further performing 
post treatment, and purifying to obtain dimethyldiallylammonium 
chloride. According to the invention, a continuous method is used, so that no evacuation problem exists, and 
nitrogen gas gap substitution is not required; through the on-line control on the pH value, the dropwise adding amount of the liquid alkali is controlled, thereby maximally relieving the 
hydrolysis of the chloropropene, improving the product yield and reducing the production of three wastes; and due to 
continuous production, all operating parameters are constant, and a DCS (
distributed control system) can be used to perform full-
automatic control. Thus, the error and deviation caused by artificial operation can be eliminated, and the product quality is more stable.