Abstract: To prepare high-performance Kappa-Carrageenan (KC)-based hydrogels, we employed ultrasonic treatment to modify KC to prepare ultrasonic modified Kappa-Carrageenan (UM-KC). Then we blended UM-KC with sodium alginate (SA) at different mass ratios, and prepared UM-KC/SA composite hydrogels by two-step crosslinking method with CaCO₃ and CaCl₂. Besides, we determined the effects of different UM-KC/SA ratio and crosslinking degrees on the water content, swelling ratio, mechanical properties (Tensile strength, elongation at break), infrared spectra, and microstructure of the hydrogel. The results demonstrate that ultrasonic treatment significantly improved the solubility of KC (p<0.05). When the mas ratio of UM-KC to SA was 1 : 2, the comprehensive performance of the hydrogel after secondary crosslinking was optimal. The composite hydrogel exhibited a water content of 93.26%, a swelling ratio of 0.45%, an elongation at break of 182.00%, and a tensile strength of 0.203 7 MPa. Infrared spectroscopy reveals enhanced rigidity in the composite hydrogels, while scanning electron microscopy (SEM) show that the hydrogel had a honeycomb-like porous structure. Therefore, the compounding of UM-KC and SA can prepare composite hydrogels with excellent properties, which offers new ideas and methods for the development of novel algal polysaccharide-based medical hydrogel dressings.