Astragalus membranaceus (HuangQi, 黄芪), commonly known as Huangqi, is a traditional Chinese medicinal herb with a long history of clinical use. Esteemed for its role in both pharmaceutical and dietary applications, Huangqi is recognized for its capacity to tonify the spleen and stomach, augment qi, and address a diverse array of health conditions. The primary bioactive constituents of Huangqi include Astragalus polysaccharides (APS), flavonoids, saponins, and alkaloids, with APS standing out as the most significant active component due to its multifaceted pharmacological properties. APS exhibits considerable promise for the development of novel therapeutics targeting various diseases. This review provides a comprehensive synthesis of the methodologies employed for the extraction and purification of APS. It further elucidates the pharmacological effects of APS in immunomodulation, encompassing enhanced immune organ indices, promotion of immune cell proliferation, stimulation of cytokine production, modulation of immunoglobulin secretion, and regulation of immune signal transduction pathways. Additionally, APS demonstrates neuroprotective, antioxidant, anti-inflammatory, and immune-modulatory effects. This review also highlights recent advancements in the application of APS as a viable substitute for antibiotics in animal production. The neuroprotective potential of APS has been substantiated through animal studies. Collectively, this work establishes a robust theoretical framework for advancing research into the structural characteristics, mechanisms of action, and clinical applications of APS.