Super-absorbent hydrogel fiber was prepared from polyacrylonitrile(PAN)-based acrylic fiber by hydrolyzing its nitrile groups. Chemical reaction of PAN and physical properties of hydrolyzed acryl/cotton blended yarn were analyzed using FT-IR spectrophotometer, wide angle X-ray diffractometer, differential scanning calorimetry, universal testing machine, and static honestmeter to discuss nitrile group substitution mechanism, microstructure of the hydrolyzed fiber, and other physical properties. Most nitrile groups of PAN were hydrolyzed to ionic groups such as carboxyl group err And the crystalline phase of the acrylic fiber was disrupted to amorphous phase after processing, but the fiber retained its original shape. Water-absorption ratio and antistatic resistance of the hydrolyzed acryl/cotton blended yarn increased greatly, but tensile strength decreased by half.