In order to reduce the harmful effects of demulsifiers on the environment and provide a green and reusable demulsifier, a magnetic carbon nanosphere demulsifier (Fe 3 O 4 /CNNs) was prepared in this study. The morphology and structure of the Fe 3 O 4 /CNNs were characterized by scanning electron microscopy, Fourier transform infrared, X-ray diffraction, and X-ray photoelectron spectroscopy. The results showed that the magnetic demulsifier has uniform particles and good dispersibility. In addition, the demulsification experiments showed that the dehydration rate could reach 92% under the optimal demulsification conditions, and the residual water content of Fe 3 O 4 /CNN magnetic demulsifier increased by 0.11% in 8 cycles of recovery experiments. The demulsification mechanism of the demulsifier was speculated. This work showed that the compounded magnetic demulsifier is friendly to the environment and is an effective material for separating oil and water phases, with broad application prospects.