Base cation transfer from stemflow is an important process for nutrient transfer and plays a key role in maintaining the balance of soil nutrient pools. To research the differences of stemflow chemistry in mixed plantations, we conducted a continuous field experiment in the rainy zone of Western China from December 2016 to November 2017. Three representative mixed plantations, including a conifer–broadleaved mixed plantation, a deciduous broadleaved mixed plantation and a multispecies mixed plantation, were selected to investigate the concentration and flux characteristics of K⁺, Na⁺, Ca²⁺ and Mg²⁺ in stemflow. The results showed that: (1) the K⁺, Na⁺, Ca²⁺ and Mg²⁺ fluxes ranged from 1.75 to 2.44 kg ha⁻¹ year⁻¹, 0.14 to 0.24 kg ha⁻¹ year⁻¹, 1.25 to 2.11 kg ha⁻¹ year⁻¹, and 0.40 to 0.60 kg ha⁻¹ year⁻¹ in these mixed plantations during the one-year observation, and the annual or seasonal (i.e., rainy or dry season) base cation fluxes in the stemflow varied slightly with the plantation types; (2) broadleaved trees had a higher average stemflow base cation contribution rate and flux-based enrichment ratio than coniferous trees, and the enrichment ratios showed a decreasing tendency with increasing trunk diameter; (3) the stemflow base cation concentration was higher in the dry season, while flux was observed to be higher in the rainy season. These results suggested that increasing the proportion of broadleaved species in mixed plantations might improve soil nutrient content and benefit material cycling in subtropical forest ecosystems.