The invention discloses a synthetic method of an aminopropionic acid-containing fluorescent brightener. The existing method can be used for improving the reaction system of a DSD acid triazine fluorescent brightener to a certain extent, but fails in improving the productivity effectively. The synthetic method of the aminopropionic acid-containing fluorescent brightener is characterized in that triple condensation raw material organic amine 3-[(2-ethoxy)amino] propionic acid derivative is completely or partially salified with DSD acid to obtain a DSD acid organic ammonium salt aqueous solution; and then mono-condensation, double condensation and triple condensation reactions are orderly performed to obtain the aminopropionic acid-containing fluorescent brightener. The reaction time of the synthetic method provided by the invention is equivalent to that of the existing preparation method; in the reaction state that the concentration of the final product brightener is 10-12%, the viscosity of the mono-condensation reaction material system is only about one tenth of that of the material system with the concentration of final product brighter of 7-8% in the existing process; and therefore, the utilization rate of the reaction equipment is improved and the production cost is reduced as much as possible.