Abstract: The protein extraction rate from Porphyra haitanensis was investigated as index to carry out high-value processing and utilization of Porphyra haitanensis. The supersonic wave extraction techniques of protein from Porphyra haitanensis were studied by single factor experiments and orthogonal method. Extraction solvent, ultrasonic time and wave power, solid-liquid ratio and pH were investigated, and the Porphyra haitanensis protein was analyzed for its spectral properties such as equielectric point, emulsification, foaming, and antioxidant activities. The optimum extraction conditions of Porphyra haitanensis protein were as follows: Ultrasonic wave power 1350 W, working time 50 min. Under these conditions, the extraction ratio of Porphyra haitanensis protein was 60.98%±1.01%. The results showed that the isoelectric point (pI) of Porphyra haitanensis protein was 4.5. At the isoelectric point, Porphyra haitanensis protein had better foam stability, reaching 80.84%±2.95%. Porphyra haitanensis protein extract exhibited an excellent antioxidant ability within 5~50 mg/mL. When the concentration was 50 mg/mL, the total antioxidant capacity was 2.89±0.09 U/mL and the scavenging capacity of ABTS⁺ radical was equivalent to 0.83±0.08 mmol/L Trolox, and the scavenging capacity of DPPH radical was 68.04%±0.73% at 10 mg/mL. This study can provide theoretical basis and technical support for the exploitation and utilization of Porphyra haitanensis resources.