Abstract: In order to further study and improve the performance of N-P flame retardants, fastgrowing poplar was chosen as the object. APP, BL and MBL are inorganic fire retardants, GUPR is organic and WR is composite material. And 10% aqueous solution of them was used to impregnate poplar under the condition of 60℃ and -005MPa,then tests of Limiting Oxygen Index （LOI）,Smoke Density Rating（SDR）,CONE were used to characterize the flameretardant effects of the specimens. Results showed that:Drugloading rate of inorganic fire retardant was higher than other two kinds of fire retardants, the LOI of specimens treated with BL and MBL was higher than 40,shows good performance.Drugloading rate of GUPR was lowest but flame resistance and smoke suppression effect were the best.Flame retardants （except the WR） reduced the thermostability and advanced the pyrolysis process of wood while postponed the peak of HRR.Pyrolysis process of WRtreated specimens were inhibited most and blocking ability of carbon layer was excellent but the inhibition of heat release rate was poor.）Compared with samples treated with BL , the Total Smoke Production of MBL decreased, the emission of the CO reduced 262% in the first 300 s and the whole burning process alleviated.