Abstract: Dendrobium is a traditional, valuable, and nourishing medicinal herb in China. It benefits the stomach, promotes fluid production, nourishes Yin, and clears heat. Polysaccharides are among the main active ingredients of Dendrobium. By reviewing literature over the past decade, the common structures and biological activities of Dendrobium polysaccharides are systematically summarized. The results illustrate that Dendrobium polysaccharides possess various effects, including antioxidant, antitumor, anti-inflammatory, and immunoregulatory effects, gut microbiota modulation, blood sugar reduction, and anticataract properties. The chemical structures of these polysaccharides are closely related to their biological activities. Previous studies suggest that polysaccharides rich in mannose and glucose exhibit stronger activity, whereas higher acetylation levels enhance immune activity. Higher uronic acid content corresponds to greater antioxidant ability, which may be due to the presence of (1→4)-α-D-Glcp and (1→4)-α-D-Manp on the main chain. Additionally, chemical modifications such as sulfation, selenization, and acetylation can enhance activity, whereas carboxymethylation decreases it. This article summarizes the research progress in recent years on the structure, biological activity, and product development of Dendrobium polysaccharides both home and abroad, elucidating the structure-activity relationship, aiming to provide important references for their in-depth development and application.