A high capacitance RuO₂-ZrO₂ coating was prepared by thermal decomposition method. Extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) and ab initio calculations were applied to understand the role of the microstructure in the acquisition of high specific capacitance of RuO₂-based oxides. The results show that the RuO₂-ZrO₂ oxide prepared at critical crystallization temperature can be considered to be quasi-amorphous or microcrystalline (A short-range ordered crystal structure can be seen from the TEM image, but no diffraction peaks can be seen from the XRD diffraction patterns). And this RuO₂-ZrO₂ was identified as a solid solution with high solid solubility. It referred to herein as a quasi-amorphous solid solution. Such a special microstructure was conducive for “synergistic catalysis” owing to the cationic interaction and thus could gain high “active site density” and high “active surface”, thus developing high specific capacitance.