Abstract: In order to endow poplar plywood with certain flame retardant properties, ammonium polyphosphate-chitosan/boron nitride (APP-CS/BN) were choosed as the flame retardant coatings, and were deposited on the plywood through layer by layer self-assembly method. The results of FTIR and SEM show that APP-CS/BN coatings are assembled on the surface of plywood to form a membrane structure, and the assembled membranes are evenly distributed on the surface of the material. Cone calorimeter (CONE) combustion tests show that APP-CS/BN self-assembled coatings effectively prolong the ignition time (TTI), reduce the heat release rate (HRR) and total heat release (THR) of the plywood, while increase the char residue which formed after combustion of the material. Compared to untreated plywoods, the ignition time of self-assembled plywoods with 15, 20, 25 APP-CS/BN layers increase by 100%, 105% and 125%, respectively; Pk-HRR is decreased by 10.15%, 22.34% and 31.82%; THR is decreased by 2.89%, 13.68% and 15.32%. The char formation rates of untreated plywood, self-assembled plywoods with 15, 20, 25 APP-CS/BN layers are 18.55%, 24.07%, 26.04% and 27.65%, respectively. In summary, the poplar plywood exhibits good flame retardant properties via layer-by-layer self-assembly flame retardant treatment. However, when the number of self-assembly layers is from 20 to 25, the increment amplitude of flame retardancy of plywood becomes slower. In this study, the suitable self-assembly coatings are 20-25 layers.