The invention discloses a continuous flow preparation method of 2,6-diethyl-4-methylaniline diazonium salt. The method comprises the steps: adding a diazotization reagent, an acid and 2,6-diethyl-4-methylaniline to an integrated reactor material feeding mouth continuously, and performing a diazotization reaction so as to obtain the 2,6-diethyl-4-methylaniline diazonium salt continuously in an integrated reactor material discharge mouth for subsequent reactions. The production process is safe and efficient, no accumulation of high-risk diazonium salt is caused, and the problem of large viscosity of a kettle reaction system is solved; and the product has high yield and purity, and the process has simple and efficient operation.