In order to simultaneously endowing the flame retardancy and toughness of poly (lactic acid) (PLA), a phosphorus containing acrylate core-shell flame retardant (P-CM) with an average particle size of about 190nm was prepared by seed emulsion polymerization using DEAMP core material, methyl methacrylate (MMA) as shell material and three allyl isocyanate (TAIC) as crosslinking agent. TEM results show that it has a typical core-shell structure. The thermal properties of PLA materials was characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The results showed that: the glass transition temperatures of the core and shell of P-CM were 13.6 ℃ and 115.6 ℃ respectively, the initial decomposition temperature (Td5%) was 263 ℃, and the residue after decomposition was 36wt%. After adding 5% P-CM to toughening and synergistic 10%App/5%β-CD flame retardant PLA, its limiting oxygen index (LOI) value was increased by 32.9%. It is worth mentioned that the toughness of modified P-CM is improved greatly, in which the impact strength increased by 182.5%, the tensile strength increased by 2.9%, and the elongation at break increased by 28.9%, respectively. The PLA material with high flame retardancy and toughness was obtained.