The invention discloses a crosslinking agent and a cross-linked polymer as well as a preparation method and an application thereof. The crosslinking agent comprises two or more acetal groups, is small in toxicity, high in stability, safe to use, and can be applied to crosslinking of a plurality of macromolecules or polymers comprising ortho-dihydroxy, meta-dihydroxy, amino, sulfydryl or the combined structural units of the ortho-dihydroxy, the meta-dihydroxy, the amino, and the sulfydryl; the cross-linked polymer is prepared by crosslinking the plurality of macromolecules or polymers comprising the ortho-dihydroxy, the meta-dihydroxy, the amino, the sulfydryl or the combined structural units of the ortho-dihydroxy, the meta-dihydroxy, the amino, and the sulfydryl using the crosslinking agent; a cross-linked material is stable in structure for long time, non-degradable, has good biocompatibility, is simple in preparation method, is low in cost, and is suitable for industrialized production. The cross-linked polymer material can be used as medical health materials, including an embolizing agent and a soft tissue repair filling agent.