【Objective】As the problem of soil acidification is becoming increasingly serious, the research of soil acidification rate appears to be of critical importance, especially on stoichiometry of mineral weathering, which plays an important role in quantifying soil acidification rate. The soils undergone intensive weathering in the subtropical region of China are highly acid-sensitive. In recent years, acid deposition has become very serious, making the problem of soil acidification prominent. Therefore, in this research, a leaching experiment with simulated acid rain was conducted to explore stoichiometric relationship between released elements during the weathering process of minerals in intensively weathered soil derived from granite in the subtropical region, in an attempt to provide a certain basis for quantitative estimation of soil acidification rate.【Method】First of all, soil samples were collected. The soil derived from granite in the subtropical region. Some of the samples were treated with EDTA-ammonium acetate solution to elute base cations adsorbed on soil colloids, which can avoid the effect of cation exchange reaction in subsequent processes of the experiment. Then the two groups of soil samples, eluted and uneluted, were leached with simulated acid rain at the same time by modified Batch. The leachates were collected for analysis of K⁺, Na⁺, Ca²⁺, Mg²⁺ and Si.【Result】(1) During the eluting process, the amount of K⁺, Na⁺, Ca²⁺ and Mg²⁺ eluted from the samples was related to the contents of exchangeable base in the soil. For highly weathered ferrisol, eight rounds of elution processes were performed to elute all the exchangeable base cations from soil colloids; (2) In the leaching process with simulated acid rain, the amount of released base cations from the eluted samples were low and stable while that from the uneluted samples varied sharply from the initial stage. A quite large amount of base cations were released at the initial stage of the leaching and did at a rapidly reducing rate with the leaching till they got quite close to the eluted samples in base leaching rate. This result indicates that the base cations released at the initial stage of leaching for uneluted-base soil came mainly from cation exchange reaction, while those released at the later stage originated from mineral weathering; and (3) During the leaching process by simulated acid rain, weathering of polyminerals in the soil mainly were feldspar, hydromica and vermiculite with releasing base cations. Based on the released amounts of base cations and Si, the stoichiometric relationships of K⁺:Na⁺:Ca²⁺:Mg²⁺ and base cation and Si (BC:Si) in horizons A, B1 and B2 of the eluted and uneluted soils were obtained. The BC:Si of the eluted soil was 0.8~1.4:1 and of the uneluted soil was 3.4~4.0:1. The sharply difference between them indicates the importance of eluted soil exchangeable base cations for accurate stoichiometric relationships of mineral weathering.【Conclusion】(1) During the base eluting process, the base cations eluted from the soil come mainly from the exchangeable base cations. Eight rounds of elution can elute this portion of base cations completely for the highly weathered soil; (2) During the process of leaching with simulated acid rain, the eluted and uneluted soils differ sharply in released amount and pattern of base cations because the base cations released come mainly from weathering of minerals for the eluted soil, while they include exchangeable base cations for uneluted soil; and (3) The main weathering polyminerals in the soils are hydrolysis of feldspar, hydromica and vermiculite as triggered by acid rain. The stoichiometric relationship of BC:Si of the eluted soil is 0.8~1.4:1 while that of the uneluted soil is 3.4~4.0:1. The sharply difference means that to achieve accurate stoichiometry of mineral weathering, it is essential to elute exchangeable base cations adsorbed on soil colloids.