Abstract: Zheng qi deficiency is the fundamental pathogenesis of malignant tumors, spanning tumor initiation, progression, invasion, and metastasis. Accumulating basic and clinical evidence confirms that Fuzheng therapy, as a core principle in traditional Chinese medicine (TCM) oncology, effectively improves patient prognosis by modulating antitumor immune responses and remodeling the tumor microenvironment. This paper innovatively proposes that Zheng qi exhibits immunological characteristics of potentiality, distribution, defensive capacity, and vulnerability. Fuzheng therapy preserves the inherent potentiality, distributive capacity, and defensive capacity of Zheng qi while correcting its vulnerability by protecting immune reserves, promoting T-cell infiltration, and remodeling the immunosuppressive microenvironment. Disruption of the innate immune barrier and insufficient activation of adaptive immunity constitute the core manifestations of Zheng qi deficiency. This paper further systematically elucidates the scientific connotations of antitumor Fuzheng therapy: consolidating the foundation and nourishing primordial qi to eliminate pathogenic factors and resolve toxins; warming and transforming phlegm turbidity to harmonize; activating blood to unblock blood stasis; resolving toxins to attack toxin accumulation; smoothing the flow of qi to relieve stagnation—with the ultimate aim of “nourishing Zheng qi so that accumulations resolve spontaneously”. These insights provide a theoretical basis for TCM in regulating tumor immunity and preventing and treating malignant tumor progression.