【Objective】In recent years, due to aggravating acid deposition and highly intensive agricultural production, involving steadily growing chemical fertilizer application rate, permanent nutrient removal with harvested crops, etc., soil acidification of farmlands is speeding up. Soil acidification of large areas of paddy fields in South China has become an important problem in rice production. Therefore how to ameliorate or remedy the acidifying paddy soil and to exposit its mechanism has become a subject of important theoretical and practical significance to rebuilding healthy soils and guaranteeing food security of the nation. Although lime has already been extensively used as soil amendment to remedy acidified soils, Long-term application of a large amount of lime would not only cause the soil to harden, but also disturb the balance between calcium, potassium and magnesium in the soil. Silicon-calcium-potassium-magnesium (SCPM) fertilizer may be used as an alternative due to its lower solubility and comprehensive nutrient supply. The purpose of this study is to make clear functions of SCPM and its effects on soil acidification in paddy fields. 【Method】A four-year stationarly field experiment was conducted to investigate effects of SCPM on soil pH, electrical conductivity (EC), exchangeable acidity, exchangeable base cation, pH buffer capacity (pHBC) and net base production in the paddy soil. The experiment was designed to have five treatments, i.e. CK (Traditional fertilization practice of the local farmers): Treatment I (CK plus 750 kg·hm^-2 SCPM); Treatment II (CK plus 1 125 kg·hm^-2 SCPM): Treatment III (CK plus 1 500 kg·hm^-2 SCPM); and Treatment IV (CK plus 1 875 kg·hm^-2 SCPM), for comparison.【Result】Results show that CK lowered soil pH in the soil layers (0~30 cm), causing soil acidification at a rate of 2.88 kmol·hm^-2·a^-1, while the SCPM treatments raised soil pH by 1.22~1.58 and 0.35~0.64 units in the topsoil (0~15 cm) and the subsoil (15~30 cm), respectively, and produced alkali in the two soil layers, as much as 9.93~13.82 kmol·hm^-2·a^-1, of which 80% was in the topsoil. Compared to CK, SCPM treatments significantly increased soil EC, exchangeable Ca²⁺, exchangeable Mg²⁺ and base saturation in the two soil layers, and soil exchangeable K⁺ in the topsoil layer, and decreased soil exchangeable acid in the two soil layers, particularly soil exchangeable Al³⁺. In the SCPM treatments, the effects became more significant with rising SCPM, especially in the topsoil layer. The exchangeable base cations and alkali released by SCPM contributed 104.3% to the total reduction of soil exchangeable acid, which suggests that it is the main path to reduction of soil exchangeable acid. In Treatments III and IV, pHBC was significantly increased or by 34.85% and 48.51%, respectively, as compared with CK, which was mainly attributed to the increase in soil cation exchange capacity.【Conclusion】 In a word, SCPM can not only effectively lower soil acidity in the top- and sub-soil layers of paddy fields, but also greatly increase soil exchangeable Ca²⁺ and exchangeable Mg²⁺ in the two layers, and soil exchangeable K⁺ in the topsoil layer. The higher the SCPM application rate, the more significant the effects. SCPM releases Ca²⁺, Mg²⁺ and alkali, which is believed to be the main mechanism of dulling soil acidification in paddy fields.