A method for preparing non-free radical photo-crosslinked hydrogels includes: dissolving component A that is a polymer derivative modified with o-nitrobenzyl phototrigger in a biocompatible medium to obtain solution A; dissolving component B that is a polymer derivative containing hydrazide, hydroxylamine or primary amine in a biocompatible medium to obtain solution B; mixing solution A and solution B to obtain a precursor solution of hydrogel; under light irradiation, crosslinking aldehyde generated from the o-nitrobenzyl with the hydrazine, hydroxylamine or primary amine to obtain a hydrogel by forming hydrazone, oxime or schiff base, respectively. A kit for preparation and application of the hydrogel in tissue repair, beauty therapy, and cells, proteins or drugs carriers is also described. The method or kit can achieve in situ photo-gelling on tissue surface or in situ forming thin gel on wounds in clinical treatment of wounds.