Built in 1959, the Zhenjiang Jianbi Power Plant is one of the main power plants in the power grid of East China. Its total power generation has hit over 100 billion kWh in the past twenty-six years. Nevertheless, a significant amount of coal ash has also been generated. To investigate the environmental effects of coal ash, the authors selected Longshan Ash Mountain and Zhenguan Ash Mountain as the study objects. Testing the samples of coal ash, surface water and its surrounding sediments, rocks, soil, and rice seed around the coal ash mountain areas, the authors have found that the topsoil in the study area is rich in selenium (Se) due to the influence of coal ash. According to the classification criteria set by Tan Jianan, 32.96% of the soil contains a medium level of Se, 43.08% is rich in Se, 7.86% is low in Se concentration, 6.76% is very low in Se concentration, and 9.34% contains excessive Se. The soil with excessive Se is mainly located around the downstream coal ash area, with a maximum amount of 14.7×10^-6. It is found that the richness of Se in the farmland far away from coal ash areas mainly stems from high Se concentration in the irrigation water, while the richness of Se in the farmland close to coal ash areas is attributed not only to irrigation but also to the sediments of coal ash brought by the water flow. The dendrogram analysis of Se and heavy metals shows that the region affected by Se is also affected by Cd, Hg and Pb. The richness of these heavy metals is ranked as Hg > Cd > Pb. The topsoil is generally not contaminated by As, Cd, Cr, Cu, Hg, Hi, Pb, Zn and other heavy metals because the concentration of these heavy metals is less than the natural amount. Only the concentration of Cd and Hg is close to the maximum of the second degree in the national farmland standard. Affected by soil environment, the study area has Se-rich rice, whose concentration of As, Cd, Cr, Hg, Pb and other heavy metals does not exceed the food contamination standard. Based on these findings, the authors suggest using different irrigation sources in the study area. Specifically, we should use Se-rich water to irrigate the Se-insufficient soil so as to expand the area with Se-rich soil, and use the average water to irrigate the Se-excessive soil so as to reduce Se concentration. The results of the study also imply that coal ash is rich in Se and contains very little harmful heavy metals. Therefore, it may be profitable to extract Se from coal ash and produce Se-rich fertilizers.