Abstract: The determination of trace nitrite with catalytic kinetic spectrophotometry was described.The principle of determination based on the NO_2~-can catalyze the oxidation and decoloration of arsenazo(Ⅰ) by KIO_3~-in H_3PO_4 medium.The linear range is 0~80.0 μg/L,and the detection limit is 0.68 μg/L.The proposed method was applied in the determination of nitrite in water samples with satisfactory.