In summary, we synthesized solution processable PANI-CSA with high optical conductivity in the mid-IR and used reversible chemical tuning to vary its doping level, ultimately enabling high-performance active metasurface thermal emitter. Through IR spectroscopic ellipsometry, we demonstrated the transition of PANI-CSA from a reflective metal with weak charge localization to a lossy dielectric neutral state. Combined with nanophotonics structure design that incorporate AFP and GSP modes at distinct wavelengths, the large refractive index modulation was used as an unconventional scheme to modulate the broadband thermal emissivity at mid-tolong IR region. Finally, the optimization and evaluation procedure considering the weightedaverage spectral directional emissivity can be directly performed with the optical properties measured from ellipsometry. We envision the understanding of PANI system and the co-design with metasurface theories will enable the development of highly efficient and multifunctional active optical materials based on the interdisciplinary research in correlated charge transport, organic chemistry, and (electro)chemical materials engineering, from nanomaterials design to device fabrication.