Janus nanoparticles are a kind of nanomaterials with anisotropic spatial or physical and chemical properties, which have attracted wide attention due to their unique properties and applications in functional coatings, environment, catalysis, biomedicine and other fields. The side-by-side distribution of different nanoparticles provides a flexible platform for customizing Janus nanoparticles with rich functions, compared with traditional homogeneous nanoparticles, functional Janus nanoparticles expand more emerging applications by two or a combination of functions. The strategies for preparing functional Janus nanoparticles which are developing rapidly at present, such as magnetic responsiveness, catalysis, asymmetric infiltration and self-actuation, are specifically discussed. At the same time, a number of applications enabled by functional Janus nanoparticles are introduced and the existing problems are analyzed. Finally, this article is concluded with future directions and outlooks with respect to both syntheses and applications of functional Janus nanoparticles in order to provide ideas for relevant researchers.