Gastric cancer remains a significant global health burden, with limited therapeutic options and poor clinical outcomes. Although conventional treatments such as surgery and chemotherapy are widely used, their effectiveness is often hindered by adverse effects and high recurrence rates, highlighting the urgent need for safer and more effective alternatives. Scleromitrion diffusum (Willd.) (S. diffusum), a well-established anticancer herb in traditional Chinese medicine, has demonstrated promising clinical potential against gastric cancer. This review systematically examines the bioactive components of S. diffusum and their multi-target mechanisms of action against gastric cancer. Key active compounds, including flavonoids, anthraquinones, and terpenoids, have been identified as exerting synergistic anti-gastric cancer effects. These compounds collectively target critical pathways in gastric cancer pathogenesis, including apoptosis induction, suppression of proliferation and angiogenesis, and immune modulation. The mechanistic elucidation presented in this review not only validates the traditional use of S. diffusum in cancer management but also provides a molecular basis for its potential application in precision medicine strategies for gastric cancer. Beyond summarizing existing evidence, this work highlights critical gaps in current knowledge and proposes essential directions for future research, providing important references for integrating traditional medicine with modern oncology approaches.