This study characterized the species diversity and biogeographical distribution patterns of the major genera of two dominant families, Lauraceae and Fagaceae, in northern tropical and subtropical forests of mainland China. The study also examined the relationship between the species diversity of these two families and those of forest communities and explored possible historical factors that affect the distributions of their species diversity. The results show that the dominant families in these forests are Lauraceae, Fagaceae, Theaceae, and Ericaceae. The species richness of both Lauraceae and Fagaceae are positively correlated with that of the forest communities where they occur, and compared to Fagaceae, Lauraceae contributes more significantly to the species diversity of the forest communities. The highest species richness of both Lauraceae and Fagaceae are found in the south-central parts in northern tropical and subtropical regions of China. The diversity centers of Cryptocarya and Beilschmiedia of Lauraceae and Castanopsis of Fagaceae are found in the northern tropical and southern subtropical regions, mainly in the southern Guangxi and southern Yunnan provinces. The diversity centers of the genera Cinnamomum, Neolitsea, Machilus, and Litsea of Lauraceae and Lithocarpus and Cyclobalanopsis of Fagaceae are found in the south-central part of the subtropical region, which corresponds to their family-level diversity distributions. However, the highest diversity of Lindera, Phoebe, and Actinodaphne of Lauraceae and Quercus of Fagaceae are found in the central and western parts of the study region. Our results indicate that ecological adaptation and biogeographical history jointly determine the current biodiversity distribution patterns of Lauraceae and Fagaceae.