Vanadium dioxide (VO2) exhibits great potential in smart windows due to its phase-transition property. Herein, polydopamine (PDA), coated on VO2 nanoparticles, is employed to replace doping to trigger the phase transition of VO2 at ambient temperature based on its photothermal effect. The VO2@PDA thin films not only can avoid optical property degradation caused by doping, but also exhibit better optical property than VO2 films due to the improved dispersion after coating PDA that the solar energy modulation (ΔTsol) is improved from 11.2 to 14.5% when the luminous transmittance (Tlum) remains unchanged. In addition, VO2@PDA nanoparticles remain stable under acidic and oxygenic condition, which is attributed to the stable PDA shell and the interfacial interaction between VO2 core and PDA shell. This work provides an novel method to replace doping treatment to promote the phase transition of VO2.