Pinus massoniana plantations have been established around the southern part of China to provide timber or fuelwood. In recent years, widely distributed monoculture P. massoniana forests have been transformed into mixed forests due to various ecological problems, such as the decrease in biodiversity in the forests and the lack of soil nutrients. However, how soil microbial diversity responds to a variety of P. massoniana mixed forests and its driving mechanisms remain poorly understood. Therefore, we examined the effect of forest conversion from monoculture P. massoniana forest to P. massoniana (CK) + native broad-leaved (Cinnamomum longepaniculatum (CL), Sassafras tzumu (ST), Toona sinensis (TS) and Phoebe zhennan (PZ)) plantations on soil microbial diversity in both spring and autumn in subtropical China. High-throughput sequencing technology was used to analyse the soil bacterial community composition and diversity in the patches of different tree vegetation types. The results indicated that Proteobacteria (32.74 ± 1.30–46.33 ± 0.49%), Acidobacteria (17.48 ± 2.95–30.17 ± 7.20%) and Actinobacteria (7.74 ± 1.14–27.62 ± 5.74%) were the predominant phyla in all patches. The diversity and richness of the bacterial community in May were higher than those in November. In all 5 patch types, TS and ST had higher soil bacterial richness and diversity than CK regardless of season. In addition, we found that the soil N and P and soil moisture of TS and ST were significantly higher than those of PZ and CK, and the RDA results showed that N appeared to be the most significant impact factor for soil bacterial diversity and richness in this study. Sequencing showed that the TS patchy plantation contained more N-fixing bacteria, such as Bradyrhizobium, Rhizomicrobium, Candidatus Solibacter and Bacillus, than the other 4 forest patches. This study suggested that constructing indigenous broad-leaved tree patches (especially TS) in monoculture P. massoniana plantations could increase soil pH and the contents of N, P and soil moisture, causing changes in habitats that favour the growth of the bacterial community, which may help enhance material circulation and nutrient cycling in soil.