This paper was to study the effects of alkali treatment， alkali-acid treatment， and screw extrusion treatment on the oil-holding capacity， water-holding capacity， swelling capacity and in vitro bile salt binding capacity of Gracilaria dietary fiber； meanwhile， differential scanning calorimeter， Fourier transform infrared spectrometer， X-ray diffractometer and scanning electron microscope were used to characterize thermal stability， molecular structure， microscopic morphology and other structures of those sample. The results showed that the content of insoluble dietary fiber from Gracilaria increased with treatment of alkali， alkali-acid and screw extrusion by 27.58%， 44.30% and 61.27%， respectively. Moreover， the dietary fiber with screw extrusion showed the highest oil-holding capacity (2.71 g/g± 0.21 g/g) and water-holding capacity (10.54 g/g±0.68 g/g). Compared with the native one， the abilities to bind sodium glycocholate and sodium taurocholate of Gracilaria dietary fiber with alkali， alkaline-acid and screw extrusion treatments were increased by 18.43%-36.40% and 7.03%-26.06%， respectively. The crystallinity and thermal stability of modified Gracilaria dietary fiber were most increased by 12.92% and 28.76 ℃ screw extrusion treatments. In addition， the alkali treatment removed some protein on the surface of Gracilaria dietary fiber， while with alkali-acid and screw extrusion treatment， cracks appeared on the fiber's surface， which increased the specific surface area and facilitated the adsorption of substances. Conclusion: Our research showed that all three pretreatments can improve the physicochemical functions of Gracilaria dietary fiber， which is related with the changed microstructure. The results can provide a theoretical reference for the development of functional food of Gracilaria dietary fiber.