Pot experiment with rice on two typical purple soils shows that in red purple soil phosphorus could reduce arsenic poisoning to rice,while the effect was just the opposite in red brown purple soil.The research on distribution of arsenic fractions clarifies that there was higher content of arsenic of different fractions in rhizosphere than in nonrhizosphere in two soils,and arsenic existed in an accumulating state in the rhizosphere.In the red purple soil,arsenic was transformed from available arsenic(Fe-As,Al-As)to relatively inavailable one(O-As)when phosphorus was added,thus reducing the biotoxicity of arsenic.While in the red brown purple soil,arsenic was transformed from relatively inavailable arsenic(Fe-As,Al-As)to available one(Ca-As,A-As)when phosphorus was added.