Cordyceps militaris (CM) is recognized as an edible, nutritional fungus. In this study describes the preparation of effervescent granules using CM and assesses the effects of different grinding particle sizes (40, 100, and 300 mesh) on their physicochemical properties and active components. The excipient ratio of the effervescent granules was optimized through singlefactor and response surface tests, and the formula was comprehensively evaluated using the appearance, formation rate, and solubility of the effervescent granules as comprehensive scoring indices. The 300-mesh CM powder exhibited a median particle size (D50) of 3.74 μm, with a bulk density of 0.31 g•mL−1, tapped density of 0.53 g•mL−1, repose angle of 48.2°, slide angle of 61.5°, water-holding capacity of 2.97 g•g−1, oil-holding capacity of 3.77 g•g−1, solubility of 50.67%, polysaccharide content of 17.82 mg•g−1, cordycepin content of 1.63%, protein content of 23.18%, and DPPH and hydroxyl radical scavenging rates of 94.21% and 41.58%, respectively. The optimal formulation for effervescent granules prepared with 300-mesh powder was determined to be 15% CM and 45% effervescent agent mass fractions and a citric acid-to-sodium bicarbonate ratio of 1.2:1. The resulting effervescent granules exhibited rapid dissolution (average disintegration time: 139 seconds), excellent flowability (repose angle: 34.7°), and superior sensory evaluation (balanced sweet-sour taste with distinctive flavor), all of which met food processing quality standards. This study effectively enhanced the product added-value of CM resources, thus providing a theoretical foundation for the development of CM-derived high-value functional foods.