High-temperature and long-term sintering of β″-Al2O3 solid electrolyte (Beta″ Alumina Solid Electrolyte, BASE) can easily cause Na2O volatilization. It reduces the solid electrolyte (SE) quality, resulting in low ion conductivity of the electrolyte. It is also difficult to form uniform ionic channels. This work designs a simple nonaqueous precipitation through de-etherification heterogeneous polymerization reaction between optimal sodium source sodium ethoxide and aluminum isopropoxide to synthesize highly active precursor powders with Na-O-Al as the skeleton, effectively reducing the synthesis and sintering temperatures of β″-Al2O3 solid electrolyte and minimizing the Na2O volatilization. Importantly, residual organic groups and a low synthesis temperature of 1150 °C promote the formation of in situ carbon uniformly. In-situ carbon with a mass fraction of about 3.98% will form uniformly distributed ion transport channels with a diameter of 1-3 μm when sintering at 1580 °C. These channels ensure a migration rate of sodium ions and ion conductivity of β″-Al2O3 solid electrolyte of 0.028 S/cm at 300 °C.