Abstract: In order to achieve high-value utilization of abandoned Porphyra haitanensis, we studied the enzymatic hydrolysis technique and antioxidant activity of P. haitanensis protein. Single factor test and response surface optimization test were used to screen the optimum protease and enzymolysis parameters based on the indices of hydrolysis degree and reducing power. The antioxidant activity of the hydrolysate was studied by determining the reducing power of hydrolysate and scavenging ability of hydrolysate on the free radicals DPPH, ·OH and\rmO_2^- ·. The results show that neutral protease was the optimal enzyme among the six enzymes. The optimal conditions for the hydrolysis of P. haitanensis proteins were as follows: substrate concentration 35 g·L^–1, enzyme dosage 31 200 U·g^–1, hydrolysis temperature 45 ℃, pH 7.6, hydrolysis time 5 h. Under these conditions, the hydrolysis degree was 31.37% and the reductive power was 2.2. The scavenging rates for DPPH, ·OH and\rmO_2^- ·were 56.26%, 85.84% and 72.74%, respectively, which indicates that P. haitanensis can be hydrolyzed by neutral protease effectively, and its hydrolysate has good antioxidant activity and application prospects.