On the basis of single factor experiment， the extraction process of Gelidium amansii ethanol extract (GAEE) was optimized by response surface methodology. Then， the GAEE was successively extracted by petroleum ether， ethyl acetate and n-butanol， and the antioxidant and antibacterial activities of different extraction phases were evaluated. The results showed that the optimum extraction conditions were as follows: extraction time was 64 min， ultrasonic power was 350 W， extraction temperature was 55 ℃， ethanol concentration was 60% and solid-liquid ratio was 1∶35. The extraction rate of GAEE was 1.654 g/g， and DPPH radical scavenging rate of GAEE (2 mg/mL) was 58.29% Subsequent experiments proved that the antioxidant and antibacterial activities of different extraction phases were concentration dependent， and the antioxidant and antibacterial activities of ethyl acetate phase were the strongest. IC50 values of ethyl acetate phase against DPPH， ABTS free radicals， and hydroxyl radical were 672.4， 14.1， 599.7 μg/mL respectively. Their minimum inhibitory concentrations(MIC) of ethyl acetate phase against Staphylococcus aureus and Vibrio parahaemolyticus were 156.3， 156.3 μg/mL， and the minimum bactericidal concentrations(MBC) of ethyl acetate phase against Staphylococcus aureus and Vibrio parahaemolyticus were 625， 312.5 μg/mL.