This study produces high-purity nano-silica from corn straw ash (biomass power plants) using an alkaline fusion derived sodium silicate solution. CO₂ replaces traditional acids in the carbonation reaction, enabling high extraction yield (93.11%). The process addresses the gap in directly utilizing combustion ash for such high-purity silica. Key optimal conditions identified were: 5 M HCl concentration, NaOH fusion reagent, 1:1.2 mixing ratio, 3 M NaOH solvent, and 12 h ripening. The resulting nano-silica achieved 92.73% purity, 10-50 nm particle size, 270 × 10⁻⁵ m³/kg DBP absorption, 55.9916 m²/g specific surface area, 6.38% LOD, and 6.69% LOI. These properties meet national standards for premium, loosely structured nano-silica. This method provides an economical and effective silicon source, reducing costs and offering economic-environmental benefits.