Multidrug-resistance (MDR) Pseudomonas aeruginosa (P. aeruginosa) is a lethal gram-negative pathogen causing hospital-acquired and ventilator-associated pneumonia, which is difficult to treat. Our previous studies confirmed that baicalin, an essential bioactive component in Scutellaria baicalensis Georgi, exhibited anti-inflammatory effects in an acute pneumonia rat model induced by MDR P. aeruginosa. However, this effect of baicalin in constrast its low bioavailability, and its mechanism of action is still unknown. Thus, this study investigated whether the therapeutic effects of baicalin against MDR P. aeruginosa acute pneumonia are owing to the regulation of gut microbiota and their metabolites using pyrosequencing of the 16S rRNA genes in rat feces and metabolomics. As a result, baicalin attenuated the inflammation by acting directly on neutrophils and regulated the production of the inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-10. The mechanisms were through down-regulation of TLR4 and inhibition of NF-κB. Furthermore, pyrosequencing of the 16S rRNA genes in rat feces revealed that baicalin regulated the composition of gut microbial communities. At the genus level, baicalin efficiently increased the abundance of Ligilactobacillus, Lactobacillus and Bacteroides, but decreased the abundance of Muribaculaceae and Alistipes. Further, arginine biosynthesis was analyzed as the core pathway regulated by baicalin via combination with predicting gut microbiota function and targeted metabolomics. In conclusion, this study has demonstrated that baicalin relieved inflammatory injury in acute pneumonia rat induced by MDR P. aeruginosa via arginine biosynthesis associated with gut microbiota. Baicalin could be a promising and effective adjunctive therapy for lung inflammation caused by MDR P. aeruginosa infection.