The investigation focuses on the effect of silicon particles (Si) and phosphorus-based flame retardants on the flame retardancy of epoxy resins. The flame-retardant properties have been studied by limiting oxygen index, vertical burning test, cone calorimeter test and micro-combustion calorimeter. The results demonstrate that Si, FR and APP can greatly improve the flame-retardant and thermal properties. It is found that the addition of Si/APP/FR can promote the formation of stable char layers, indicating the condensed-phase effect of the flame retardants.