Abstract: The vinyl-terminated oligophosphate hybrid monomer (VOPP) was synthesized by step-reaction polymerization using phenyl dichlorophosphate(PDCP), ethylene glycol(EG), methanol, hydroxyethyl methylacrylate(HEMA), VOPP and styrene (St) by graft copolymerization preparation of phosphorus element of hybrid monomer grafted polystyrene copolymer (VOPP-co-St). The structural characteristics and average molecular weight of VOPP were explored by FTIR and gel permeation chromatography(GPC).The thermal stability and flame-retardant properties of the VOPP-co-St were evaluated by TGA, limit oxygen index(LOI) and microscale combustion calorimeter; The morphology and composition of the char layer were investigated by SEM and XPS. The thermal decomposition activation energy(E_a) of VOPP-co-St was calculated by Flynn-Wall-Ozawa(FWO) method. The results show that the temperature of maximum decomposition rate, residual mass and LOI of VOPP-co-St increase with the increase of VOPP content, peak heat release rate(PHRR) and total heat release(THR) reduce with the increase of VOPP content, and droplet phenomenon disappeare, while E_a increases with the increase of degradation conversion rate.