The invention discloses a salt-sensitive flocculating agent as well as a preparation method and application thereof. The salt-sensitive flocculating agent is 2,4-di(p-aminobenzoyloxy)-[1,3,5]-triazine-6-starch ether and is prepared through the following steps: uniformly mixing p-aminobenzoic acid, sodium hydroxide and cyanuric chloride; adding de-ionized water; raising the temperature to room temperature and regulating the pH (Potential of Hydrogen) value to be 4.6, so as to obtain white sediment; filtering, and drying and grinding a filter cake to obtain a white intermediate, i.e., 2,4-di(p-aminobenzoyloxy)-6-chloro-[1,3,5]-triazine; then mixing starch, the sodium hydroxide, the 2,4-di(p-aminobenzoyloxy)-6-chloro-[1,3,5]-triazine and dimethyl sulfoxide; heating, stirring and cooling to room temperature; adding ethanol and separating out a product; filtering and drying to obtain the salt-sensitive flocculating agent, i.e., the 2,4-di(p-aminobenzoyloxy)-[1,3,5]-triazine-6-starch ether.The salt-sensitive flocculating agent disclosed by the invention is used fro removing anionic dyestuff in dyestuff wastewater, and the salt-sensitive flocculating agent can be regenerated and cyclically used in a salt solution after being used for flocculating the dyestuff, so that the wastewater treatment cost is reduced and the regenerated flocculating agent can be cyclically used for a plurality of times.