Magnetic nanoparticles have the advantages of large surface area，high saturation，low toxicity and good magnetization，etc.，and have high application value in many fields. In recent years，the development of magnetic nanoparticles is more and more rapid. However，due to the disadvantages of magnetic nanoparticles in the application process，such as the high surface effect of magnetic nanoparticles，in the solution，there is likely to be aggregation reaction，so its application is limited. The physicochemical properties of magnetic nanoparticles can be improved by proper modification，which not only improves the stability and degradability，but also significantly improves the biocompatibility and enhances its application value. Based on the surface modification function of magnetic nanoparticles，this paper discusses the application of magnetic nanoparticles in environmental separation and biological separation，and looks forward to the development prospect of magnetic nanoparticles in the future.