Soil acidity is a serious constraint to food production worldwide, soil degradation caused by soil acidification has become a global consensus. The impact factors of soil acidification were complex, landscape pattern is an important influential factor of ecological process, but the relationship between landscape pattern and soil acidification is not well understood. In order to discover the spatial and temporal patterns of farmland topsoil pH and watershed landscape, and to quantitatively examine the impacts of landscape pattern on farmland soil acidification. in this paper the Liuxihe watershed was selected as the study area and soil sample buffer as the research unit based on 759 farmland topsoil samples and land use pattern in 2010, distribution map of soil pH in 1980s, and the research methods included landscape pattern index analysis, spatial analysis and correlation analysis. The results showed that: 1) The watershed was dominated by acidic soil in 2010, soil mean pH was 5.79, 86.03% of the samples and 97.3% of the farmlands with pH<6.5; Soil pH were in an order of irrigated cropland (6.03)>irrigated paddy fields (5.68)>dry cropland (5.62), and in an order of alluvial soils (5.92)>paddy soils (5.84)>latosolic red earths (5.66)>purplish soils (5.55)>yellow earths (5.40)>red earths (5.39). 2)Soil acidification was significant during 1980—2010, soil pH decreased in 31.23% of the samples and 33.76 km2 (24.76%) of the farmlands; Soil acidification in paddy fields and dry cropland were significant (pH reduction rate>27%), and irrigated farmland soil pH showed an increasing trend. Soil pH decreased in 92.21% of yellow earths and 54.31% of red earths. Except alluvial soils with an increasing trend of pH, farmland soil acidification was significant in other soils, among of which yellow earths was most significant, followed by red earths. 3) Farmland soil pH was increased and the distribution became more complicated from the upper reaches to lower reaches. pH were lower in the upper reaches, two side of middle reaches and the east sides of the lower reaches, acidic soil was spread outwards during 1980—2010 and soil acidification was obvious. Soil pH increased in complex pattern in the middle of middle reaches and the west side of lower reaches. 4)Except dry cropland, significant correlation were found between landscape metrics of different land use types and soil pH in shrubbery land, grass land and bare land. Soil pH was positively correlated with the densities of water area and road. The destruction of natural forest, the fragmentation of paddy fields, garden plots and water, scattered distribution of impermeable construction land may increase the risk of soil acidification while large area of water renewal and agglomeration of paddy fields may reduce it. These conclusions are useful for the control and remediation of farmland acidification.