The invention relates to the field of adhesives and in particular relates to an adhesive for a fiberboard. The adhesive is prepared from the following components in parts by weight: 100 to 400 parts of water, 10 to 50 parts of polyvinyl alcohol, 200 to 600 parts of rubber latex, 10 to 50 parts of polyethylene glycol 400 and 500 to 1500 parts of silica sol. The invention further discloses a preparation method of the adhesive for the fiberboard. According to the adhesive, characteristics that natural latex has a strong cohesive force and large molecular weight and the silica sol has good wettingperformance and small molecular weight are utilized, and inorganic and organic molecules are connected through heating reaction, so that the storage period, the sizing performance, the gluing strength, the waterproof performance and the environment-friendly performance can reach the requirements of glue for aldehyde-free fiberboards The production cost is low and economic benefits are obvious.