Abstract: Taking porphyra haitanensis as raw material, the composite enzymatic extraction technology was used to extract soluble dietary fiber, the antioxygenic activity of the soluble dietary fiber of porphyra haitanensis for lard and vegetable oilwas study. Based on single factor experiments, extraction conditions of soluble dietary fiber in porphyra haitanensis were optimized through quadratic regression orthogonal design. A quadratic regression orthogonal model was established to express the relationship between soluble dietary fiber yield (Y) and four factors including dosage of cellulase (X1) , enzymolysis pH (X2) , enzymolysis temperature (X3) , and enzymolysis time (X4) . Results showed :The optimal extraction paraneters were :dosage of cellulase 1.1%, enzymolysis pH5.8, enzymolysis temperature 55℃, and enzymolysis time 1.5h. Under such conditions, the highest yield of soluble dietary fiber, which was 9.80% ±0.12%. The expansive capacity and water holding capacity were 1.97mL/g and 276%, respectively. The soluble dietary fiber of porphyra haitanensis could significantly slow POV value rising trends of oils and fats, and had a certain amount of time and concentration dependent.Prompt with antioxidant activity of the soluble dietary fiber of porphyra haitanensis.