The invention provides a fiber humidity adjusting board. The fiber humidity adjusting board is obtained by soaking a composite board in a humidity adjusting liquid, and the composite board is composed of a fiber material treated by carboxylation and porous inorganic particles dispersed in the fiber material, wherein the mass of the inorganic particles accounts for 5 to 30 percent of the solid content of the fiber, and the inorganic particles adopt one or the combination of silica gel, clay, concavo-convex rods, diatomaceous earth, activated carbon, wood charcoal and bamboo charcoal. The invention has the advantages that the fiber humidity adjusting board is a precise humidity adjusting product, when the ambient humidity changes, response can be rapidly made, and through moisture absorbing and releasing, the ambient humidity can be balanced, so as to maintain the humidity in the environment to be constant and ensure that the phenomena of wetting, mould damage or drying and cracking of the stored articles can not occur within the adjusting environment. A strap-shaped fiber humidity adjusting board is adopted, which can be cut arbitrarily; the humidity adjustment can be performed in function, and the moisture holding amount can reach and surpass the equivalent international humidity adjusting products. The fiber humidity adjusting board adopts non-toxic, harmless and recoverable raw material, and the fiber humidity adjusting board is a new-generation green and environment-friendly product.