Abstract: Impacts on the extraction yield of pineapple pomace soluble dietary fiber (SDF) of factors of water bath method and ultrasonic method. And on the basis of single factor experiment, these optimal conditions for extracting soluble dietary fiber (SDF) of pineapple pomace by orthogonal experiment methods of ultrasound was established. In addition, using IR, SEM and XRD to structuralize and check antioxidant which was extracted from the ultrasonic extraction of the pineapple pomace soluble dietary fiber (SDF) . The result showed as follow:pH5, ultrasonic temperature 60℃, solid-liquid ratio of ultrasound 1 ∶20g·mL-1, ultrasonic time 45min. Under the optimal condition the SDF yield was 15.91%. The pineapple pomace soluble dietary fiber (SDF) IR spectra of slag appeared a strong round bottom absorption on peak around 3404cm-1, pineapple pomace soluble dietary fiber (SDF) had high purity and high crystallinity. Furthermore, form the SEM, pineapple pomace soluble dietary fiber (SDF) presented a more structured block structure, which was consistent with the XRD results. At the same concentration, the antioxidant activity of pineapple pomace SDF was better than that of pineapple pomace, but lower than the commercial synthetic antioxidant (BHA) .