The invention relates to a fiber porous material preparation method. The method is characterized in comprising the following steps: (1) fiber is pretreated with a steam explosion method, such that fiber supramolecular structure is broken, intramolecular hydrogen bond breakage degree is improved, and fiber polymerization degree is reduced; (2) the fiber is dissolved in a NaOH water solution under a low temperature, such that a viscous solution is formed; (3) reinforcing fiber and a pore-forming agent are added under stirring, such that a uniform mixture is obtained; (4) the mixture is subjected to a coagulation bath, such that fiber is regenerated from solvent, and the pore-forming agent produces pores, such that a spongy fiber product is produced. The method provided by the invention has the following advantages: an alkali solution is adopted as fiber solvent, such that solvent price is low; the process is short; production period is short; cost is low; and chemical reagent usage is reduced.