Gastric cancer (GC) is the second leading cause of cancer-associated deaths worldwide. Tanshinone IIA (TSN) is the pure extract from the root of red-rooted salvia and has been reported to inhibit the progression of GC cells. In this study, we investigated the microRNA (miRNA) mediated gene repression mechanism in TSN-administrated GC condition. The cell viability of GC was determined by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay. Cell migration and invasion were detected by transwell assays. The expression levels of epithelial-mesenchymal transition (EMT)-associated proteins (N-cadherin, vimentin, E-cadherin), High-mobility group box proteins 2 (HMGB2), β-catenin pathway-related proteins (β-catenin, c-myc, cyclin D1) were detected by western blot analysis in TSN/GC. The expression patterns of miR-874 and HMGB2 in GC were determined by quantitative real-time polymerase chain reaction (qRT-PCR). The potential miR-874-targeted HMGB2 was searched via bioinformatics methods and identified by dual-luciferase reporter assays, RNA immunoprecipitation (RIP) assays, and RNA pull-down assays. Xenograft tumor model was used to evaluate biological function in vivo. TSN limited the proliferation, migration, invasion, EMT progression in GC, and these results could be inverted by the silencing of miR-874. Moreover, the putative binding sites between miR-874 and HMGB2 were predicted by starBase software online. Meanwhile, enforced expression of HMGB2, negatively correlated with that of miR-874, reversed the positive effects of TSN administration on cells. Mechanically, TSN restrained the GC progression by miR-874/HMGB2/β-catenin signaling in vitro. Additionally, in vivo experiments confirmed that TSN inhibited the GC progression as well. TSN restrained the GC progression by regulating miR-874/HMGB2/β-catenin pathways in vitro and in vivo.