Blumea balsamifera(L.) DC., a perennial herb in the Asteraceae family native to China and Southeast Asia, has a notable history of medicinal use due to its pharmacological properties. Using UPLC–Q–Orbitrap HRMS techniques, we systematically investigated the chemical constituents of this plant. A total of 31 constituents were identified, of which 14 were flavonoid compounds. Significantly, 18 of these compounds were identified inB. balsamiferafor the first time. Furthermore, the mass spectrometry fragmentation patterns of significant chemical constituents identified inB. balsamiferawere analyzed, providing important insights into their structural characteristics. The in vitro antioxidative potential of the methanol extract ofB. balsamiferawas assessed using DPPH and ABTS free-radical-scavenging assays, total antioxidative capacity, and reducing power. The antioxidative activity exhibited a direct correlation with the mass concentration of the extract, with IC50values of 105.1 ± 0.503 μg/mL and 12.49 ± 0.341 μg/mL for DPPH and ABTS, respectively. For total antioxidant capacity, the absorbance was 0.454 ± 0.009 at 400 μg/mL. In addition, the reducing power was 1.099 ± 0.03 at 2000 μg/mL. This study affirms that UPLC–Q–Orbitrap HRMS can effectively discern the chemical constituents inB. balsamifera, primarily its flavonoid compounds, and substantiates its antioxidative properties. This underscores its potential utility as a natural antioxidant in the food, pharmaceutical, and cosmetics sectors. This research provides a valuable theoretical basis and reference value for the comprehensive development and utilization ofB. balsamiferaand expands our understanding of this medicinally valuable plant.