We report light-assisted iodine ion migration in CuI – a popular wide bandgap p-type semiconductor, which was synthesized via iodinating Cu film in iodine solution. In-depth crystallographic analysis was performed with the combination methods of X-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), crystal modeling and diffraction simulation. The samples show strong diffraction peaks of γ-CuI, yet still exists β phase diffraction. Loop current-voltage (IV) test shows characteristics of resistive random access memory (RRAM), suggesting the existence of large amount of movable native defects, which forms the conductive filaments. UV irradiation was found to be effective to convert the RRAM device from low resistance state (LRS) to high resistance state (HRS), indicating potential application of novel memory device with electric read-in and optical erasure function. To study the properties of native defects, time-lapsed PL were employed, in which the near band edge defects luminescence, related to V_Cu, increased, whereas mid-band broad luminescence, related to V_I, decreased, with the increase of irradiation time. UV irradiation induced defects evolution was also observed in X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). Finally, we propose the microscopic physical mechanism of defect migration in CuI with the assistance of UV irradiation. This work reveals the nature of point defects evolution in CuI under light irradiation and is expected to arise more discussions on defects formation, migration and light-defects interaction of CuI material.