Abstract: The layer-by-layer of self assembly (LBL) method was adopted to construct CH-APP flame retardant coating by alternating adsorption of cationic chitosan (CH) and anionic ammonium polyphosphate (APP) on the surface of sisal fiber cellulose microcrystal (SFCM), and (CH-APP)_n/SFCM flame retardant composites were prepared. The structure and properties of the (CH-APP)_n/SFCM composites were measured by Zeta potential analyzer, FTIR, TGA, POM, vertical flame testing (VFT), SEM. The results of Zeta potential show the surface of SFCM potential is positive and negative in the alternately adsorption process, which indicates the CH-APP coating is successfully coated on the surface of SFCM. POM and SEM reveal a thick coating was covered on the surface of the SFCM by LBL and the surface of SFCM becomes more rough. With the increase of the number of CH-APP self assembled layers, the initial decomposition temperature(T_5%) of (CH-APP)_n/SFCM composite reduces from 279.4℃ to 243.1℃, and the char residue of (CH-APP)_n/SFCM composite increases from 11.24% to 32.06%. The results of VFT show that (CH-APP)_n/SFCM composites present outstanding flame retardancy after LBL method and the (CH-APP)_n/SFCM composite with 10 layers assembled exhibits the best flame retardancy with self-extinguishing fire flame retardant.