Phthalazinone is a critical structural factor for high-performance polymer material, which is achieved by polar structure and the structure characteristic of unsymmetrical and kink non-coplanar. In this study, a novel phthalazinone-based epoxy (EEPZ) has been designed and synthesized. The rheological behaviors, thermal stability and combustion behaviors of cured systems have been investigated by dynamic rheology, TGA, DMA, UL-94 vertical burning and cone calorimetry tests. It was found that the phthalazinone-based EEPZ epoxy resin had the lower melting viscosity within broader processing window and enhanced char forming ability for bisphenol A epoxy/4 ' 4-diamino-diphenyl sulfone (E44/DDS) system. When combined with only 20 wt% EEPZ in the E44 system, the E44/20%EEPZ/DDS, passed the UL-94 V-0 rating. In the combustion test, the total heat release, total smoke production and peak of heat release rate were sharply respectively decreased by 44.7%, 24.3% and 44.6% in the case of E44/20%EEPZ/DDS compared with E44/DDS. The results of morphology characterization chemical structure and component for residue char in EEPZ epoxy resin confirmed that the phthalazinone group can lead to form nitrogen-containing compact char layer during combustion. The combined technologies (TGA-FTIR, Py-GC/MS) was utilized to detect the pyrolysis process of the crosslinks system and the charring mechanism. Simultaneously, the tensile strength and tensile modulus of the composites were also improved. [GRAPHICS] .