Abstract: Traditional bird survey methods require a large number of experienced ornithology experts and the time and the space that can be covered are limited. Passive acoustic monitoring (PAM) provides a new approach for bird diversity assessment, and it is non-invasive, suitable for long-term monitoring and data can be stored permanently. To explore the effectiveness of PAM in assessing bird diversity in subtropical forests, this study conducted traditional line transect surveys and PAM across seven regions in Lishui, Zhejiang Province, from 2020 to 2023. Acoustic data were processed using a combination of manual and AI-assisted identification to obtain bird species composition and acoustic bird diversity indices (species richness R_SN, diversity index R_H, richness index R_R, evenness index R_J, bird index R_V), and six soundscape indices (acoustic complexity index ACI, bioacoustic index BI, acoustic entropy index H, normalized difference soundscape index NDSI, acoustic diversity index ADI, acoustic evenness indices AEI) were calculated. The results showed that: (1) A total of 177 bird species were recorded by the two methods combined, with species recorded by both methods accounting for 58.19%, and each method uniquely recorded 37 species, indicating that acoustic monitoring effectively supplements traditional surveys by detecting overlooked species; (2) The correlations between soundscape indices and acoustic bird diversity indices exhibited significant seasonal differences, with the strongest correlations in spring (15 significant pairs) and the weakest in summer (3 significant pairs), among which the BI performed most robustly on the overall scale; (3) The bird species richness and acoustic bird index calculated from acoustic data showed consistent ranking across the seven regions, effectively distinguishing bird diversity levels among different habitats. In conclusion, PAM can effectively obtain bird species composition information, and acoustic bird diversity indices show potential for biodiversity assessment, but the application of soundscape indices requires consideration of seasonal differences. This study provides scientific basis and practical reference for applying PAM in biodiversity monitoring and assessment in subtropical regions.