Sodium alginate (SA) hydrogel has broad prospects in medical dressings due to its good biocompatibility and non-toxicity. However, the shortcomings of a single SA hydrogel, such as insufficient toughness and poor antibacterial properties, limit its large-scale application. In this study, SA/CNC–[email protected]/TA (SACT) hydrogels were prepared using CNC–[email protected] and tannic acid (TA) with different contents into SA. The results show that the addition of CNC–[email protected] improves the toughness of the gel, and the addition of TA, and the fracture strain is further improved, and get to 128% form 8% of SA and 78% of SAC. Simultaneously, the antibacterial analysis using the zone-inhibition and colony-counting method shows that the composite hydrogel has decent antibacterial effects on both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This work demonstrates a new method for improving the toughness and antibacterial properties of SA hydrogel, which is expected to be used in medical dressings and other relevant fields.