The effects of UV irradiation on the chemical structure, thermal stability, surface morphology, and mechanical properties of aramid fibers were systematically studied. Changes in the chemical structure and thermal stability of the aramid fibers were characterized using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis, respectively. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray wide-angle diffractometry (XRD) were employed to observe the surface morphology and crystal structure transformation of the aramid fibers before and after UV irradiation, respectively. Finally, the mechanical properties of the fibers were characterized using a monofilament strength testing machine. The FTIR results showed that the aramid fiber surfaces were photodegraded after UV irradiation, and new oxygen-containing functional groups appeared. The SEM and AFM results revealed that the surfaces became rough and gullied after ultraviolet irradiation. XRD results showed that UV irradiation had little effect on the crystal structure of the aramid fibers. Finally, the tensile properties indicated that the tensile strength decreased with increasing irradiation time. Based on these results, the surface chemical activity and roughness of the aramid fibers were increased after UV irradiation, which improved the interface adhesion between the aramid fibers and composite matrix while enhancing the interface force. Thus, solving the bottleneck problem of high-performance fibers, which are difficult to weave and exhibit poor composite strengths, is important. This study provides a reference for further expanding the application of aramid fibers in the field of composite materials. These applications include high-protective clothing and protective upperwear, which require enhanced interface adhesion.