The composites were synthesized by the reaction of Bi(NO3)3·5H2O, KI, and MoS2 and were prepared with different molar ratios of Bi/Mo (1:5, 1:2, 1:1, and 4:1) by altering the amount of bismuth nitrate pentahydrate. The phase composition and chemical bonds of the composites were characterized via X-ray diffraction and FT-IR, and the morphologies of the samples were characterized via scanning electron microscopy. With the increase of lanthanum source, the lamellar structure of the sample surface became more and more obvious. The results showed that the phase composition of the composites with different ratios of Bi/Mo was different. When the Bi/Mo reached 4:1, the composite material was Bi2MoO6/BiOI. The heterojunction structure formed between Bi2MoO6 and BiOI effectively promotes the separation of photogenerated electrons and holes and improved the photocatalytic activity. Therefore, the effect of the composites on the degradation of RhB was better than pure BiOI under the irradiation of a 350-W xenon lamp.