In the previous field surveys, the arsenic (As) concentration in many soils from farmland ecosystems in the karst area of Guangxi exceeded the maximum reference value of the current standard. The fate and mobility of As in paddy ecosystems are controlled by the following processes: (1) adsorption and desorption of As, (2) coupled redox reaction of Mn, Fe, and As, and (3) precipitation and dissolution of As-bearing iron oxides. It is difficult to distinguish how each individual process contributes to the overall As releasement under field conditions. However, numerical model can provide an alternative approach for cost-effective evaluation of Individual progress controlling As releasement as long as the general field parameters were given. Here, we selected two typical research areas from a typical karst basin in Hengxian, Guangxi. One is near Zhenlongjiang river and composed of Quaternary sediments (Yunbiao, YB) and the other locates on the Devonian in the center of a karst basin (Maling, ML). The basic physical and chemical properties of the soils were characterised. Adsorption experiments of arsenite (As (III)) and arsenate (As (V)) on the soils including adsorption kinetics, adsorption isotherms and pH edges were conducted to evaluate the adsorption capacity of the soil and provide parameters for the surface complexation model (SCM). Redox cycling experiments consisting of a reduction period (0~20d), an oxidation period (20~30d) and a second reduction period (30~50d) were performed to simulate the coupled adsorption and redox processes under flooding and drainage conditions in the paddy fields. The species and concentrations of As, Fe, and Mn in the aqueous and solid phases were analyzed at the selected time. Adsorption experiments showed that: (1) As (V) adsorption kinetics was faster than As (III); (2) the adsorption capacity of the soils in ML was higher than that in YB because of difference in Fe and Mn concentrations; (3) in YB, the adsorption capacity of the soils from the dry land was significantly lower than that from the paddy field, whereas such phenomenon was not observed in ML; Redox cycling experiments showed that (1)the concentration of As in the liquid phase decreased in ML while the concentration of As increased in YB paddy soils probably due to difference in the contents of Mn in the first reduction period;(2) the trends were the same afterwards, showing that the immobilization of As was strengthened in the oxidation period and the release of As in the second reduction period was enhanced. In the future research, the variation of arsenic species during the redox cycles will be analyzed to better understand the processes that will influence As releasement during agricultural irrigation management in the paddy fields. In addition, a numerical model coupling As adsorption and redox reactions of As, Fe and Mn will be established to simulate As releasement during redox cycles.