In this study, a maleimido-substituted aromatic s-triazine (TMT) was synthesized successfully via the nucleophilic substitution reaction between cyanuric chloride and N-(4-hydroxyphenyl) maleimide (HPM) formed from paraaminophenol and maleic anhydride; and its structure was characterized by flourier transform infrared spectroscope (FT-IR), 1H and 13C nuclear magnetic resonance (NMR), and elemental analysis (EA). The studied flame-retarded epoxy resins were obtained via thermal curing reactions among 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) modified epoxy prepolymer (DOPOER), 4,4′-diaminodiphenyl ethane (DDM) and TMT. Cure kinetics, flame-retardant, thermal and mechanical properties of the cured epoxy resins were characterized by differential scanning calorimeter (DSC), thermogravimeric analysis (TGA), limited oxygen index (LOI) measurement, UL 94 vertical burning test and mechanical test. The results indicate that TMT can promote the curing reaction of epoxy resins and decrease its apparent activation energy (Ea). Introduction of TMT can greatly improve flame-retardant, thermal and mechanical properties of the cured epoxy resins. Compared with the DOPOER/DDM system without TMT, LOI value of the cured epoxy resin can increase from 36.4% to 51.8%, and all samples can pass UL 94 V-0 rate when TMT content ranges from 1.98 wt% to 7.44 wt%. Its initial degradation temperature and glass transition temperature (Tg) can increase maximally by 37.6 °C and 12.6 °C, respectively when TMT content is 3.88 wt%.