Abstract: Using Geographical Information System(GIS) and data from 38 sampling sites in hilly red soil croplands, the spatial and temporal distribution characteristics of pH were investigated. The results indicate that average soil pH decreases by 0.94 and pH decreasing area is 645.9 km² in 20 years. pH decreases in the range of 1.0～2.0, and is mainly distributed in soils derived from phyllites, granites and red sandstones, with approximately areas of 296.1 km², 136.2 km² and 42.2 km² respectively. pH increasing soil area is 24.1 km², and is largely distributed in soils derived from purple shale,which area is approximate 11.3km². Based on soil type, areas with decreasing pH are the water loggogenic paddy soils; elevation wise, areas with increasing pH are below 300 m, though areas with the highest decrease in soil pH generally lies below 300 m or between 500 m and 300 m. Correlation analysis shows that change in pH is negatively correlated with initial pH and positively correlated with elevation, organic matter and clay content. Change in pH in these regions can be predicted based on multilinear regression models.