Abstract: In order to further improve the flame retardant performance of epoxy resin, FR-PN@ETPTA flame retardant microcapsules with ethoxylated trimethylpropane triacrylate (ETPTA) as the shell and phosphorus-nitrogen flame retardant (FR-PN) as the core material were prepared by microfluidic technology and applied to epoxy resin (EP). The thermal stability, flame retardancy and mechanical properties of FR-PN/EP and FR-PN@ETPTA/EP were compared. The effects of FR-PN@ETPTA flame retardant microcapsules on the combustion performance and thermal degradation behavior of EP were discussed, and the flame-retardant mechanism of FR-PN@ETPTA flame retardant microcapsules was revealed. The results show that the flame retardancy of EP is improved by flame retardant microcapsule. When the amount of flame retardant microcapsule is 10wt%, the limiting oxygen index (LOI) value increased to 37.3%, and the UL-94 reached V-0. The tensile and flexural properties of epoxy resin are reduced by adding FR-PN or flame retardant microcapsules, but the tensile and flexural properties of the specimens with flame retardant microcapsules are better than those with flame retardant. After adding 10wt% flame retardant microcapsules, the impact strength of the resin increases by 39% than that of pure EP. The results show that the flame-retardant mechanism of flame retardant microcapsule modified epoxy resin is the combination of gas phase flame retardant and condensed phase flame retardant.