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Optimizing nitrogen utilization efficiency and mitigating nitrogen losses in cows plays a pivotal role in fostering economic sustainability within contemporary agricultural systems. Biochanin A (BCA), a natural component in red clover, has the potential to improve nitrogen metabolism in dairy cows. The primary objective of this study was to probe the impact of biochanin A supplementation on lactational performance, nitrogen metabolism, and blood metabolites in dairy cows. A complete randomized block design experiment was conducted over 28 d, involving 36 multiparous Holstein cows (comparable milk yield = 37.1 ± 2.90 kg, BW = 642 ± 70.0 kg, days in milk = 92 ± 8.0 d, and parity = 2.4 ± 0.50), which were allocated to three treatment groups: the control group (with 0 g/d BCA), the low group (with 10 g/d BCA), and the high group (with 40 g/d BCA). Biochanin A supplementation improved the lactational performance of cows by increasing milk yield by 6.3% (P= 0.007) and feed efficiency by 12.7% (P= 0.009). Total intestinal apparent digestibility was unaffected by BCA supplementation (P> 0.05), but microbial nitrogen was increased by 30.0% (P= 0.002) for promoting nitrogen utilization efficiency by 20.7% (P= 0.004). Milk competent yields (protein, lactose, and non-fat milk solid) were increased with increasing BCA supplementation (P< 0.05). Urea nitrogen levels in plasma and milk were both decreased by BCA supplementation (P< 0.05). Blood routine parameters and plasma biochemical parameters both received no effect by BCA supplementation (P> 0.05). BCA did not affect body health of dairy cows. Additionally, none of the plasma endocrine hormones were affected (P> 0.05). A total of 95 significantly different metabolites were screened from the plasma metabolites of cows in the BCA-added and non-added groups. After performing an enrichment analysis of the metabolic pathways associated with the different metabolites, six specific pathways were identified: bile acid biosynthesis, aspartate metabolism, pyrimidine metabolism, arginine and proline metabolism, the urea cycle, and ammonia recycling. The inclusion of BCA is suggested to enhance milk yield and modulate nitrogen metabolism by influencing relevant metabolites within the metabolic pathways.