Abstract: A new type of coupling agent Azido-Benzimidazole (ABI) containing benzimidazole and azide groups was designed and prepared in this study.And ABI was added into the domestic aramid fiber Ⅲ(DAF-Ⅲ)/polytriazole (PTA) composites to reinforce their interfacial properties.The results of SEM,Attenuated Total internal Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and XPS show that ABI can bond with the fiber by intermolecular hydrogen;FTIR and DSC results indicate that the azide group in ABI can react with alkynyl in PTA and take part in the curing process synchronously.The mechanical performances of DAF-Ⅲ/PTA composite are improved greatly after ABI modification.The Inter Laminar Shear Strength (ILSS) and flexural strength increase by 62.0% and 43.7% respectively after 2.1wt% ABI treatment compared with those of untreated composites.