The invention provides a slow release type polyphosphate curing agent, a preparation method and application thereof in preparation of a sodium silicate cured product. The preparation method comprises the steps that silica sol is added to a polyving akohol aqueous solution to obtain a polyving akohol intermediate product, then the polyving akohol intermediate product and polyphosphate are mixed to obtain a polymer packaged polyphosphate curing agent, and fiannly spray drying is performed to obtain the slow release type polyphosphate curing agent. Accoridng to the slow release type polyphosphate curing agent, the preparation technology is relatively simple, the product stability is high, the adaptability is good, and the storage life is long; the adaptation period is long after a lot of the curing agent (50%) and sodium silicate are mixed, the mixture uniformity and the fluidity are good, and various construction methods of pouring, mould pressing, coating and the like are convenient; the defect that the usage amount of the ordinary curing agent is small is overcome, the usage amount of the slow release type curing agent is increased, influences to the adaptation period and the construction operation of the curing agent and sodium silicate mixture are small, the alkali content in the cured product can be reduced greatly, the curing integrity is improved, and the usage performance of the cured product is enhanced.