The invention discloses an environment-friendly high-strength water-resisting and mildew-resisting adhesive for a plywood and a preparation method of the environment-friendly high-strength water-resisting and mildew-resisting adhesive. The environment-friendly high-strength water-resisting and mildew-resisting adhesive is prepared from the following raw materials including polyvinyl alcohol, cassava starch, dibutyl phthalate, sodium pyrosulfite, tannic acid, jade powder, calcium silicate hydrate, asbestos powder, p-hydroxybenzoic acid hydrazide, diammonium hydrogen phosphate, hydroquinone, sodium diethylhexyl sulfosuccinate, triethyltin chloride, phenyl mercury oleate, borax and the like. The polyvinyl alcohol and the cassava starch are subjected to a cross-linking reaction so that crystallization degrees of the polyvinyl alcohol and the cassava starch are reduced and a new cross-linking structure is formed, and furthermore, the thermal stability of the adhesive is improved; the borax is added and the polyvinyl alcohol and the starch can be subjected to further cross linking, so that the cross-linking degree and the initial viscosity of the adhesive are improved, and furthermore, the water resistance and the bonding force of the adhesive can be improved; the triethyltin chloride, the phenyl mercury oleate, the p-hydroxybenzoic acid hydrazide and the like are added so that the mildew-resisting capability of the plywood can be improved.