To optimize the ethanol extraction conditions of floridoside and to investigate the effect of floridoside on the myofibrillar protein freezing denaturation of grass crap surimi during frozen storage. Ethanol concentration, extraction temperature, extraction duration and liquor to material ratio were optimized by response surface methods. The salt-solubility of myofibrillar protein, sulfhydryl content, and Ca²⁺-ATPase activity, etc in surimi after being frozen for 6 weeks were detected. Results showed that the optimal extracting condition for floridoside was 72.3% ethanol with liquor to material ratio of 14:1 (mL/g), the extracting tempreture was 60℃, and the extracting time should be 4 h. Under these optimal conditions, the highest extraction ratio was 3.48%. Salt-soluble protein, sulfhydryl group contents, Ca²⁺-ATPase activity were effectively enhanced, and the water loss was decreased by addition of floridoside in surimi. After 4 weeks frozen, salt-soluble protein and sulfhydryl group contents were enhanced by 30.62% and 32.80%; Ca²⁺-ATPase activity in myofibrillar proteins was reduced by 37.51% in 10% floridoside treated group, while the water loss ratio was 133.07% lower than that of the control group. This study indicates that floridoside can effectively prevent myofibrillar protein denaturation during frozen storage.