In the present paper, a model based on the arsenic absorption of the unicellular microorganism tetrahymena pyriformis from the incubation aqueous solution of feed additive arsanilic acid and its degradation products As(Ⅲ) and As(Ⅴ) was established for the investigation of the environmental impacts of feed additive arsanilic acid on the living organisms. The tetrahymena pyriformis was incubated in the incubation aqueous solution and its degradation products for 72 h, after cleaning to remove the incubation aqueous solution, the cell was broken up and separated. The cell membrane and cytoplasm were digested with nitric acid and hydrochloric acid separately. A method of arsine generation atomic fluorescence spectrometry was used for the determination of the absorbed arsenic. Experimental findings illustrate that arsenilic acid and its degradation products As(Ⅲ) and As(Ⅴ) can be absorbed by the cell membrane then enter into cytoplasm. In addition, the degradation products As(Ⅲ) and As(Ⅴ) would more easily be absorbed than the arsanilic acid. The living organisms would be poisoned via the As absorption of the cells.