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Responsive Pickering emulsions, with unique nanoparticle interfaces and sensitivity to external stimuli, significantly enhanced the stability and applicability of Pickering emulsions. Multifunctional composite material poly((2-(dimethylaminoethyl methacrylate)-b-(acrylate cyclodextrin))/Fe3O4nanoparticles, namely P(DMAEMA-b-A-CD)/Fe3O4, with both multiresponsive characteristics and emulsifying capabilities had been designed to remove small oil droplets from water. Using the reversible addition–fragmentation chain transfer (RAFT) method, diblock polymers P(DMAEMA-b-A-CD) were grown in a controlled manner on the surface of Fe3O4. The Fe3O4core showed responsiveness to a magnetic field, and the block copolymers prepared via the RAFT method demonstrated reactivity to both pH and CO2. The P(DMAEMA-b-A-CD)/Fe3O4nanoparticles exhibited the capability to form Pickering/Oxford emulsions with exceptional stabilization properties. It could be observed that the introduction of CO2, acid, and a magnetic field led to the breakage of the emulsion, while the emulsion could be restabilized by removing the CO2and the magnetic field or by adding alkali. Measurements of interfacial tension, ζ-potential, and contact angle demonstrated that the emulsification/breakdown mechanisms associated with pH and CO2/N2were related to the surface wettability of the nanoparticles. In addition, the emulsifier had an excellent cycling capacity with at least 10 cycles by CO2/N2. Additionally, P(DMAEMA-b-A-CD)/Fe3O4nanoparticles exhibited excellent stability in oil phases with large polarity differences and various real oil phases with different viscosities. Importantly, the P(DMAEMA-b-A-CD)/Fe3O4nanoparticles could serve as functional materials for efficiently separating small oil droplets from water through the application of a magnetic field. Therefore, P(DMAEMA-b-A-CD)/Fe3O4nanoparticles held promising potential as materials with economic and commercial value for oil–water separation applications.