Use chlorinated 1-carbamoylmethyl-3-vinyl imidazole ionic liquid [CmVIM]Cl and tetrabutylammonium chloride (TBAC) as solvents to dissolve microcrystalline cellulose (MCC) and add different flame retardants melamine phosphate (MP), ammonium polyphosphate (APP) and nano-silica (SiO2) are used to prepare flame retardant fiber composite materials. The dissolution process of MCC was observed by polarizing microscope, and the structure, crystallinity, thermal stability and morphology change of regenerated MCC were characterized by FT-IR, XRD, TGA and SEM.The flame retardancy was tested by vertical combustion test, limiting oxygen index (LOI) and thermogravimetric analysis. The results showed that the dissolution temperature was 90 ℃, the content of TBAC was 8%, the dissolution rate of MCC was up to 6.3%, and the degree of polymerization was reduced to 505 when the solution was 25 min. MCC fractional crystallization structure into the amorphous structure, the crystallinity decreased from 74.0% to 46.4%; The thermal decomposition temperature decreased from 310 ℃ to 262 ℃, and the maximum weight loss rate decreased from 2.6%/min to 1.4%/min.The MCC surface changed from smooth and flat rod structure to uneven irregular structure. When m(MP)：m(APP)：m(SiO2)=1∶2∶2, the limiting oxygen index (LOI) of the flame retardant fiber composite increases to 33.5%, and the vertical combustion level is V-0.