Rhizosphere fungal communities are of critical importance for forest health. Microbial diversity varies with forest types due to tree species. In order to examine the influence of forest types and species composition on fungal community diversity in rhizosphere soil, the field sampling was conducted in the pure and mixed forest stands of Castanopsis hystrix in a subtropical region of China. Soil samples were taken from four forest types: Castanopsis hystrix pure forests (CH), Castanopsis hystrix × Pinus elliottii mixed forests (CHPE), Castanopsis hystrix × Michelia macclurei mixed forests (CHMM), and Castanopsis hystrix × Mytilaria laosensis mixed forests (CHML), and the species composition and structure of rhizosphere fungal community were examined by using high-throughput sequencing approach for 18S rRNA genes. The results showed that the amount of OTUs (operational taxonomic units) were 288, 331, 334 and 293 in CHML, CHMM, CHPE and CH stands, respectively, and these fungal communities were affiliated with 13 phyla, 28 classes, 85 orders, 87 families, and 131 genera. The fungal diversity was greater in CHMM and CHPE stands than in CH stands. The compositions were similar in CHMM and CHPE stands while those were significantly different in CHML and CH stands. The cladograms and co-expression network analysis showed that Ascomycota, Basidiomycota, Mortierellomycota and Rozellomycota were the dominant phyla. The study results implied that mixed forests might have a high potential for improving the microbial community diversity with formation of key species of microbial taxa due to the favorable microclimate and quality of litter composition occuring in mixed forests.