Composite flame retardant and preparation method thereof and application to production of flame retardant plywood

The invention relates to the technical field of wood processing, in particular to a composite flame retardant and a preparation method thereof and application to production of a flame retardant plywood. The composite flame retardant comprises the following raw materials in parts by weight: 25-35 parts of dicyandiamide, 30-40 parts of borax, and 30-40 parts of boric acid. All the raw materials of the composite flame retardant have synergistic flame retardant effect, have the advantages of good flame retardant effect, low poison, good smoke inhibition performance and friendly environment, and are low in cost; the flame retardant plywood, prepared by using the composite flame retardant can prominently improve the flame retardance, can achieve the requirement of national standard fireproof grade C; and the bonding strength and the maximum failure load of the flame retardant plywood are both near the bonding strength and the maximum failure load of a plywood prepared by not using the flame retardant.