The work aims to study the effects of silane coupling agent (KH-550) treated wood powder and microcapsulated red phosphorus (HP) flame retardant on the properties of wood-plastic composites. Poplar wood powder, low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and HP were taken as the raw materials. Double blending granulation and injection molding methods were adopted to prepare wood plastic composites (WPC). Through melt flow rate (MFR) test, tensile test, TGA spectra analysis, Kissinger dynamics analysis and SEM microscopic observation, the properties of the WPC were investigated and analyzed. Using KH-550 treated wood powder increased the MFR of the system by 0.01 g/min, and the maximum displacement of the systems by 2.59 mm. The HP addition increased the 5% and 50% decomposition temperature of WPC by 18 ℃ and 54 ℃ respectively. The apparent activation energy of WPC co-modified by KH-550 and HP at 420 ℃ to 500 ℃ (the main decomposition stage) was 153 kJ/mol. KH-550 treated poplar wood powder can effectively improve the tensile properties of the system. When the 10% (mass fraction) HP is added, the flame retardant effect of WPC is significantly improved.