Nanosheet BiOI materials were prepared by using the precipitation-hydrothermal method. Moreover, nanoparticle AgI/BiOI nanosheet composites were prepared using an ion-exchange method and by controlling the amount of BiOI. The phase composition, optical morphology, and absorption properties of the samples were determined using XRD, SEM, XPS, TEM, HRTEM, and UV-Vis diffuse reflectance. Organic dyes, such as methyl orange (MO) and Coomassie brilliant blue R-250 (CBB), were used to check the photocatalytic performance of the composites when undergoing photodegradation in visible light. The prepared composites had high purity, and the AgI nanoparticles were evenly loaded on the flower-like BiOI nanosheets, and both can absorb the visible light. The photocatalytic activity of sole BiOI or AgI was poor, whereas that of the composites was much better. The composite with 50% AgI exhibited the best photocatalytic activity because of the formation of a p-n heterojunction, which promotes the separation of photogenerated carriers and makes AgI stable under visible-light irradiation.