Barley is gaining popularity worldwide due to its health-promoting properties and germination can effectively enhance its function through enrichment of some phytochemicals, such as phenolic compounds. To better explore the potential of barley seedling as a functional food ingredient, in the present study, the profile and in vitro antioxidant properties of phenolic compound extract from barley germinated under NaCl stress were investigated. A total of 37 kinds of phenolic compounds were identified in phenolic compound extract by a liquid chromatography-tandem mass spectrometry system. Meanwhile, phenolic compound extracts at a concentration of 30 μg/mL significantly improved the viability of H2O2-treated HepG2 cells and maintained the cell membrane stability. These effects can be attributed to the reduction of intracellular reactive oxygen species level and enhancement of the expression and activity of some key antioxidant enzymes. Notably, addition of phenolic compound extracts up-regulated the nuclear factor erythroid 2-related factor 2 antioxidant responsive element signaling pathway, thereby leading to the increase of activities of glutathione peroxidase, superoxide dismutase, catalase and heme oxygenase-1 by 27.21%, 24.61%, 61.71% and 50.43%, respectively. In conclusion, the present study can provide a novel perspective on understanding the molecular mechanism responsible for antioxidant capacity of barley seedling.