To investigate the inhibitory effects of cultivated Dendrobium huoshanense polysaccharides (cDHP) on tumor growth in Lewis lung carcinoma (LLC)-bearing mice, a mouse model of lung cancer was established using LLC cells. The effects of cDHP on various parameters including mouse growth, tumor mass, tumor growth inhibition ratio (treatment/control, T/C), and the proliferative capacity of spleen lymphocytes were assessed. Additionally, changes in the percentage of tumor cell apoptosis, composition of spleen immune cells (T cells, Treg cells, B cells, dendritic cells, and macrophages), and levels of serum cytokines (CEA, IL-1β, IL-10, IL-2, TNF-α, VEGF, and TGF-β) were monitored. The high-dose (369.00 mg/(kg•d)), medium-dose (184 mg/(kg•d)), and low-dose (92.25 mg/(kg•d)) cDHP groups exhibited T/C ratios of 64.52%, 50.47%, and 37.68%, respectively. In lung tumor-bearing mice, cDHP demonstrated antitumor effects through an increase in the percentage of tumor cell apoptosis, enhanced proliferative capacity of spleen lymphocytes, regulation of spleen immune cell composition, and modulation of serum cytokine levels. These findings indicate that cDHP influences tumor growth through multiple mechanisms. The findings of this study provide experimental evidence supporting the potential development of antitumor drugs based on cDHP.