CdMoO₄/g-C₃N₄/GO composites were first synthesized by a hydrothermal process for the photocatalytic degradation of rhodamine B (RhB) under visible light illumination. The findings show that CdMoO₄ is highly dispersed onto g-C₃N₄ and graphene oxide (GO) sheets. The surface area of the composite increased 27–30.5 times that of CdMoO₄, and its band gap energy decreased by about 1.26 times. These features significantly improve the photocatalytic activity of the composite in the RhB decomposition reaction under visible light. The RhB degradation efficiency of the CdMoO₄/g-C₃N₄/GO composite is 5.7, 1.36, and 1.65 times that of CdMoO₄, CdMoO₄/g-C₃N₄, and CdMoO₄/GO composites, respectively. The active species trapping experiments show that the main forms in RhB degradation are •O₂–, •OH, and h+. The stability of the photocatalyst is retained even after the 5th reuse. In addition, RhB degradation products were identified with the high-performance liquid chromatography-mass spectrometry method, and the pathway of photocatalytic degradation was also addressed.