In order to understand hydrochemical compositions characteristics of different runoffs in the source region of humid subtropical basin under the background of acid deposition, hydrochemical compositions of the stream water, soil water and groundwater were analyzed in the Dinghushan forest region on a seasonal basis from 2019 to 2020. The results showed that the pH value and acid neutralization capacity (ANC) of stream water, soil water and groundwater in Dinghushan forest region were low, which were between 3.45-6.77 and -545.51-302.09 μmol H⁺/L, respectively. The stream water, soil water and groundwater were all weakly acidic. Under the influence of long-term acid deposition and natural acidification process, soil, vegetation and dust particles in the Dinghushan forest region had low buffering capacity of acid deposition, and had little effect on slowing down water acidification. The concentrations of chemical components in different water bodies were different, which were related to soil nitrification, soil adsorption, mineral chemical weathering, etc. There were little difference in the ratios of cation molar concentrations between stream water and groundwater. The cation of soil water was mainly Ca²⁺, and the molar concentrations of K⁺+Na⁺ and Mg²⁺ were relatively low. NO₃^-+SO₄^2- predominated in the molar concentration ratios of anions and DSi in the three kinds of water bodies, the molar concentration ratios of DSi and Cl^- were relatively small. The concentrations of K⁺, Ca²⁺, NO₃^- and SO₄^2- in soil water were significantly higher than those in groundwater and stream water. Except for NO₃^- concentration, there were no significant differences in K⁺, Ca²⁺ and SO₄^2- concentrations between groundwater and stream water. The concentrations of Na⁺, Mg²⁺, Cl^- and DSi in groundwater were significantly higher than those in soil water and stream water. There was no significant difference in Cl^- concentration between soil water and stream water, but there were significant differences in Na⁺, Mg²⁺ and DSi concentrations. The hydrochemical compositions type of stream water was NO₃^- · SO₄^2--Ca²⁺ · Mg²⁺, and the hydrochemical compositions types of soil water and groundwater were NO₃^--Ca²⁺·Mg²⁺. The cationic of stream water were mainly from the chemical weathering of silicate minerals and atmospheric input, which contributed 85.76% and 14.24%, respectively. The content of SO₄^2- in stream water was not much higher from that of rainwater, but the content of NO₃^- in stream water was much higher than that of rainwater, indicating that more nitrate nitrogen was leached from forest ecosystem. This study can provide basic data for study of the influence of acid deposition on hydrochemistry compositions of water bodies in source region of basin, and also provide reference for the management of Dinghushan forest region.