Abstract: Epoxy resins were modified by ammonium polyphosphate (APP) and its combination with different contents of melamine (MA) and triazine carbon-forming agent (CFA). The effects of flame retardants with different proportions(total content of 40wt%) on the rheological, curing, thermomechanical, mechanical and flame-retardant properties of epoxy resins were investigated systematically. The optimized flameretardant epoxy resin was used to fabricate glass fiber reinforced epoxy composite (GFRC), and the mechanical as well as flame retardancy of the resulting GFRC were studied. The results show that the epoxy resins modified by APP-MA and APP-CFA combinations do not show apparent synergistic flame retardancy effects, but the ternary APP-MA-CFA system (30wt%APP-5wt% MA-5wt%CFA) demonstrates superior synergistic flame retardancy effects. Compared with the unmodified epoxy resin, the epoxy resin modified by APP-MA-CFA exhibits an increase in limit oxygen index (LOI) from 18% to 50.2%, a 84% decrease in peak heat release rate (PHRR) and a 78% decrease in total hear release (THR). With the addition of flame retardants in the epoxy matrix, the GFRC shows deteriorative mechanical properties, especially for interlaminar shear strength. Again, the GFRC based on the epoxy matrix modified by APP-MA-CFA presents the best flame-retardant performance. Compared with the unmodified GFRC, the modified GFRC shows an increased LOI (from 22.8% to 66.0%), a decreased PHRR (from 354 kW/m² to 93 kW/m²) and a decreased THR (from 49.3 MJ/m² to 22.8 MJ/m²).