The MCNOs/CdS photocatalysts with different magnetic nanosized carbon (MCNOS) loads (0%, 1%, 3%, 5%) were prepared by hydrothermal synthesis. It was characterized by XRD, SEM, FT-IR, XPS, UV-Vis and VSM. The influence of MCNOs loading ratio on RhB performance and mechanism of catalyst in visible light degradation was investigated. The results show that MCNOs can effectively improve the photocatalytic effect of CdS. The degradation rate of 3%MCNOs compound is 96%, which is 30% higher than that of pure CdS. Magnetic analysis shows that it has good paramagnetism and can realize effective recovery of catalyst. The first-order reaction kinetic line of MCNOs/CdS photocatalyst degradation of RhB under visible light has a good degree of fit, indicating that the prepared catalyst has good catalytic activity.