Liubao tea is a type of traditional Chinese tea, belonging to the dark teas. This study is a basic research of the contained polyphenols (active substances) and detected preventive effects of polyphenols of raw Liubao tea (PRLT) on mouse gastric injuries induced by HCl/ethanol. High-pressure liquid chromatography was used to analyze the components of PRLT. Furthermore, a mouse gastric injury model was established to observe the preventive effects. PRLT was shown to contain gallic acid, EGC (epigallocatechin), catechin, caffeine, EC (epicatechin), EGCG (epigallocatechin gallate), GCG (gallocatechin gallate), and ECG (epicatechin gallate). The results of the in vivo study indicate that PRLT can inhibit the observed increase of gastric juice volume and decrease of gastric juice pH caused by gastric injury. PRLT can decrease the serum levels of IL-6 (interleukin-6), IL-12 (interleukin-12), TNF-α (tumor necrosis factor-α), and IFN-γ (interferon-γ) in mice with gastric injuries. Moreover, it can also increase the serum levels of SS (somatostatin) and VIP (vasoactive intestinal peptide) and reduce the serum levels of both SP (substance P) and ET-1 (endothelin-1). PRLT was also shown to increase SOD (superoxide dismutase) and GSH (glutathione) levels and decrease MDA (malondialdehyde) level. The detection of mRNA and protein in gastric tissues indicates that PRLT could also up-regulate the expression of Cu/Zn-SOD (copper/zinc superoxide dismutase), Mn-SOD (manganese superoxide dismutase), CAT (catalase), nNOS (neuronal nitric oxide synthase), and eNOS (endothelial nitric oxide synthase) and down-regulate the expression of both iNOS (inducible nitric oxide synthase) and COX-2 (cyclooxygenase-2). Thus, PRLT possess a good preventive effect on gastric injury, which is directly related to the contained active substance. PRLT show good anti-oxidative and preventive effect in gastric injury and offer promising application value.