Abstract: To improve the utilization of by-products of the Hyriopsis cumingii, this study investigated the effect of Hyriopsis cumingii polysaccharide (HCP) on the proliferation and migration of normal cells, as well as its reparative effects on ultraviolet radiation-B (UVB)-damaged cells. First, HCP was isolated and purified using DEAE Cellulose-52 column chromatography, Sephadex G-100 column chromatography and nanofiltration. Then, structural analysis was conducted using high-performance liquid chromatography, high-performance gel permeation chromatography, and infrared spectroscopy. Following this, cell proliferation experiments, cell scratch tests, UVB damage experiments, and protein expression analyses were employed to explore the anti-UVB damage effects and corresponding mechanisms of polysaccharide components. The results indicated the three substances obtained by isolation and purification were all homogeneous polysaccharide components. Among them, HCP-2 played a major role in promoting cell proliferation in HCP and facilitated the migration of HaCaT cells. The recovery of UVB-damaged cell vitality was raised by the increasing concentration of HCP-2. Furthermore, the reparative effect was more substantial than the protective effect at the same sample concentration. It was also observed that HCP-2 up-regulated the expression of the anti-apoptotic protein bcl-2 while inhibited the expression of apoptosis-related proteins casp9, p-Akt, and p-p38, indicating that HCP-2 could repair HaCaT cells by regulating apoptosis of cells damaged by UVB. In conclusion, HCP had the ability to inhibit cell apoptosis which provide a theoretical basis for its future application in the development of food and health products.