Abstract: A sand stabilization technology was proposed using filamentous fungi and wheat bran. The growth conditions of fungal mycelium were optimized through single-factor experiments and response surface methodology, while the water stability and environmental impact of the reinforced soil were evaluated using disintegration and leachate toxicity tests. Experimental results revealed that temperature was found to have a significant influence on fungal growth during the early curing stage, while nutrient solution concentration played a more prominent role during the later stages. In contrast, moisture content exerted a consistent and significant effect throughout the entire curing process. Based on the desirability function method, the optimal curing conditions for fungal-reinforced soil were determined to be a temperature of 25 °C, moisture content of 10%, and nutrient solution concentration of 10 mg/L. Compared to untreated samples, the incorporation of fungal mycelium resulted in maximum increases of 78.8% in peak strength and 369.2% in elastic modulus. The reinforced sand also exhibited significantly improved water stability, with a disintegration ratio of zero after 14 days of immersion and minimal environmental impact from the leachate. The experimental results confirm that the sand reinforcement technique based on filamentous fungal growth holds practical potential for applications in shallow soil stabilization and coastal slope protection.