It discloses a sustained release grouting material, a preparation method and an application thereof; the sustained release grouting material comprises a water swelling core and a water-soluble sustained release coating, the water swelling core is composed of bentonite, SAP and xanthan gum, which is granulated by disc granulator relying on the cohesiveness of xanthan gum; the water-soluble sustained-release coating is prepared by mixing water-soluble starch, polyvinyl alcohol, poloxamer, lubricant and plasticizer with deionized water to obtain a film-forming solution, and the film-forming solution is coated on a coating machine; the invention uses a coating machine to coat a layer of slow-release coating on the surface of the water-absorbing expansion core, and adjusts the coating thickness by controlling the mass ratio of the coating film-forming liquid to the water-absorbing expansion core particles, so as to realize the controllable water absorption onset time of the expansion core.