Abstract: Oxidation of sodium alginate (OSA) with high molecular weight and different oxidation degree was prepared by water-ethanol and water-n-propanol system, then the poly-acrylamide (PAM) cross-linked network structure was introduced. The OSA/PAM composite hydrogel was obtained by the two-step method. The effects of the volume fraction of HCl on the molecular weight of OSA as well as the influence rules of the amount and reaction time of oxidant (sodium periodate NaIO₄) on the oxidation degree were investigated under different reaction conditions.The results show that the molecular weight of oxidized sodium alginate can reach 170 000 when the volume fraction of hydrochloric acid is 24vol% in water-n-propanol system. Adjusting the addition of NaIO₄ and the reaction time can control the variety of oxidation degree of OSA in the range of 10%-85%. Based on this, the swelling and mechanical experiments of OSA/PAM composite hydrogels were studied, showing that the swelling rate of OSA/PAM composite hydrogel with 10% degree of oxidation is 1 777% after 48 h and the breaking strength is 0.11 MPa. In addition, with the increase of the degree of oxidation of OSA, the swelling rate of OSA/PAM composite hydrogel increases and the tensile strength decreases.