Elephantopus tomentosus (ET) Linn. was reported to be an anti-tumor plant. However, the chemical composition of ET and its anti-tumor compounds and potential mechanisms still unclear. In this paper, UPLC-Q-TOF-MS/MS was firstly used to identified the ingredients in ET and UPLC was used to determine the main compounds of ET. Network pharmacology was applied to predict the potential mechanisms of anti-liver cancer. Anti-tumor nuclear activate compounds and targets of ET were obtained and the anti-liver cancer effect was validated on HepG2. Finally, Molecule docking, RT-qPCR, and western blotting were used for verification of the relationship between nuclear activate compounds and nuclear targets and the potential anti-cancer mechanisms. The result showed that 42 compounds were identified in ET, which consisted of sesquiterpene lactones, flavonoids, and phenylpropanoid compounds. Scabertopin (ST), chlorogenic acid, Isochlorogenic acid B, Isochlorogenic acid A and Isochlorogenic acid C were identified as main compounds and were determined as 0.426%, 0.457%, 0.159%, 0.701%, and 0.103% respectively. 24 compounds showed high pharmacokinetics and good drug-likeness. 520 overlapping targets of the ET compounds and liver cancer were collected. The targets were used for KEGG and GO analysis. GO enrichment analysis suggested that the targets of 24 active compound closed related to promote apoptosis, inhibit proliferation, and regulate oxidative levels. KEGG enrichment analysis suggested that pathway in cancer was enriched most and p38 MAPK/p53 signaling pathway, which closely related to promoting apoptosis and inhibiting proliferation. Compounds-targets analysis based on the parameter of Betweenness, Closeness, Information, Eigenvector, Degree, and component content indicated that ST was the nucleus anti-tumor active compound of ET. HepG2 was first used to validated the anti-tumor effect of ST and the result showed that ST significantly inhibited HepG2 proliferation with a low IC50 less than 5 µM. Nucleus active compound targets, including TP53, CASP3, BCL2, EGFR, TNF-a, IL-1ß, and IL-6 were enriched based on degree value of PPI analysis. Molecule docking suggested that ST showed a good combination to TGFBR1 with the combination energy less than - 5 kcal/mol. RT-qPCR result also suggested that ST significantly medicated the mRNA expression level of TP53, CASP3, BCL2, EGFR, TNF-a, IL-1ß, and IL-6. Protein expression of p-p38/p38 and p-p53/p53 notable increased by ST treatment. In conclude, combining with UPLC-Q-TOF-MS/MS qualitative analysis, UPLC quantitative analysis, network pharmacology analysis, molecule docking, and in vitro experiments on HepG2, we suggest that ST is an anti-tumor ingredient of ET, which may target to TGFBR1 and promote apoptosis and inhibited proliferation of HepG2 by activating p38 MAPK/p53 signaling pathway. ST can be regarded as a quality marker of ET.