The invention discloses fluorescent salix mongolica 
regenerated cellulose fibers and a preparation method thereof. The preparation method comprises the following steps: peeling off salix mongolica, crushing, sieving, 
drying and cooling to prepare salix mongolica wood 
powder; extracting salix mongolica 
cellulose by adopting an 
ethanol-acid 
mixed solution; treating the salix mongolica 
cellulose by processes of 
steaming, bleaching and the like to prepare salix mongolica pulp; filtering, decompressing and de-foaming water-soluble up-conversion nano particles and the salix mongolica 
cellulose to obtain a 
spinning solution which is uniformly mixed; and 
spinning the 
spinning solution by a condensation bath, drafting and molding, refining and 
drying to obtain the fluorescent salix mongolica 
regenerated cellulose fibers. A preparation process of the water-soluble up-conversion nano particles comprises the following steps: firstly, synthesizing hexagonal-phase up-conversion luminous nano particles UCNPs by adopting a high-temperature 
thermal decomposition method; treating the UCNPs with nitrosonium 
tetrafluoroborate NOBF4, and replacing 
oleic acid molecules on the surface; finally, reacting with a hydrophilic hyperbranched 
polymer to obtain the water-soluble up-conversion nano particles. According to the fluorescent salix mongolica 
regenerated cellulose fibers, the water-soluble up-conversion nano particles and the salix mongolica regenerated cellulose are used as raw materials and are subjected to efficient blending and wet-process spinning to prepare the regenerated cellulose fibers with the excellent fluorescent performance.