<p>Aramid III is a high-performance heterocyclic aramid fiber obtained by modifying the Kevlar ^@ molecular chain. Compared the with Kevlar^@ fiber, Aramid III has higher mechanical properties, interfacial properties, and UV resistance. The work investigates the relationship between fiber structure and properties by heat-treating Aramid III under an air atmosphere at different temperature conditions and compares their performance with industrial fiber heat-treated under a nitrogen atmosphere. It is found that when subjected to heat treatment in an air atmosphere, as the temperature increases, the crystallinity of the fibers gradually increases, the surface groove structure of the fibers gradually decreases and becomes smooth and uniform, the oxygen content on the fiber surface increases and generates more –C–O– groups, thereby endowing the fibers with better surface properties, improving theTSIF and ILSS of Aramid III, and benefiting the improvement of the interfacial properties of fiber-reinforced resin matrix composites. However, when the heat treatment temperature exceeds the critical value, it can lead to a decrease in fiber toughness, as well as a significant reduction in the tensile strength, resulting in reduced performance of the TSIF and ILSS.</p>