Tetrahydropalmatine (THP) is the main component of the Chinese medicine Corydalis yanhusuo, which has been reported to alleviate limb ischemia-reperfusion-induced acute lung injury (LIR-ALI). This study aimed to investigate the mechanism underlying the effect of THP on relieving LIR-ALI. LIR-ALI model was established in rats with the presence or absence of THP pretreatment. Then, BEAS-2B cells and THP-1 macrophages were cocultured with rat serum from the Sham group and the Model group in the presence or absence of THP pretreatment. Subsequently, lung/body weight and lung wet/dry ratio of rats were calculated. Histological changes of lung tissues were observed by hematoxylin-eosin staining. Expression of CD86 and CD163 in lung tissues of rats was assessed by quantitative reverse transcription polymerase chain reaction, immunohistochemistry staining, and flow cytometry analysis. Levels of inflammatory cytokines were measured by enzyme linked immunosorbent assay. The expression of proteins related to toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB)/NLRP3 signaling was detected by western blot analysis. Results revealed that THP significantly relieved LIR-ALI in rats. Moreover, THP also reduced CD86 expression but elevated CD163 expression in lung tissues of rats with LIR-ALI. Furthermore, THP inhibited inflammation in serum and bronchoalveolar lavage fluid of rats with LIR-ALI and inactivated the TLR4/NF-κB/NLRP3 signaling in vivo. Additionally, coculture of serum from rats in the Model group also reduced viability, promoted inflammation, inactivated TLR4/NF-κB/NLRP3 expression in BEAS-2B cells and inhibited macrophage polarization, while these effects were all reversed by THP treatment. Collectively, THP could induce the polarization of M1 macrophage to M2 to suppress inflammation via inhibiting TLR4/NF-κB/NLRP3 signaling, thereby attenuating LIR-ALI. © 2022 Wiley Periodicals LLC.