Characteristics of Arsenic adsorption in red soil,in Zunyi,Guizhou,affected by pH were studied in this research work.Results show that with increase in Arsenic concentration in the soil solution,Arsenic adsorption of the soil increased,while its adsorption rate declined,high-energy adsorption sites began to gradually replace low-energy adsorption sites in absorbing As,and the absorbing reaction rate reduced.The isotherm adsorption could be well fitted by the Langmuir equation.Soil pH was an important factor that affected adsorption and desorption of Arsenic.Acid environment (pH=4~6.5) facilitated adsorption of Arsenic while alkaline environment (pH=7~8.5) did desorption of Arsenic.