The ultrasound-assisted extraction was applied to the extraction of polyphenols from the Cyclobalanopsis glauca fruit shells. The effects of the concentration of ethanol, solid-liquid ratio, ultrasonic time, and number of extraction cycles on the yield of phenolic yield were studied, and the extraction process was optimized by response surface methodology (RSM). Then the in vitro antioxidant activities of Cyclobalanopsis glauca shell fruit extract (CGSE), including ferric ion reducing antioxidant power (FRAP) and oxygen radical absorbance capacity (ORAC), were evaluated. Results: The optimal extraction process were as followed: volume fraction of ethyl alcohol 50%, extracting time 25 min, solid-liquid ratio 1:40, extraction times 5. Under condition, the maximum extraction yield was 3.13%. The Cyclobalanopsis glauca Shells Extracts (CGSE) showed higher antioxidant activity with FRAP values of (984.44±123.15) mg FeSO₄/g·DW, and ORAC values of (200.15±23.24) mg Trolox/g·DW, which was higher than the commercial antioxidant 2,6-di-tert-butyl-4-methylphenol (BHT). The above results suggest that the Cyclobalanopsis glauca fruit shell might be a natural antioxidant resource.