Abstract: Soluble dietary fiber (SDF) was extracted from wheat bran by ultrasonic pretreatment-citric acid assisted subcritical water extraction (USWEC). The effects ofultrasonic pretreatment power, citric acid/wheat bran liquid-to-soild ratio, subcritical water extraction (SWE) temperature and time on extraction yield of SDF were investigated by using single factor experiments. On this basis, the response surface optimization method was further designed to optimize the extraction process parameters. The results showed that the extraction conditions were optimized as follows: Ultrasonic pretreatment power 195 W, citric acid/wheat bran liquid-to-soild ratio 39:1 mL/g, SWE temperature 179 ℃ and time 30 min, and the SDF extraction yield was 41.00% ± 0.29%. Therefore, the developed method in this study can greatly improve the extraction yield of SDF, which has the advantages of short extraction time, green and environmental protection. This study provides a technological reference for industrial production of SDF from wheat bran.