Abstract: In mass ratio of 10:2:1, sodium borohydride, sodium acetate and copper sulfate were weighed and mixed homogeneously, and a portion of 0.20 g of the mixture was encapsulated in a small capsule to prepare arsenic detection reagent Ⅰ. In mass ratio of 1:0.25:2.5:7.5:10, silver nitrate, polyvinyl alcohol (PVA-1788), nitric acid, ethanol and water were weighed and mixed homogeneously to prepare arsenic absorption solution Ⅱ. Phosphoric acid and potassium dihydrogen phosphate were weighed in mass ratio of 1:10 and mixed well, and the mixture was dried at 105℃ for 1-2 h. The dried podwer (0.30 g) was taken and pressed into tablets, which were packed into a capsule to prepare arsenic detection reagent Ⅲ. The water sample (25 mL) and arsenic detection reagent Ⅰ were added into the reaction tube of the multi-function sample processor, and the mixture was shaken well for dissolution. Then 0.15 mL of arsenic absorption solution Ⅱ was added into 5 mL of common white spirits (40-60 degree), and the mixture was added into the absorption tube. Arsenic detection reagent Ⅲ was added into the reaction tube, which was quickly connected to the absorption tube with a connecting tube. After reaction for 5 min, air was passed though at a flow rate of 0.2 L·min^-1 for 5 min, and the absorption liquid was transferred into a colorimetric cell and its vector chromaticity was measured immediately at the wavelength of 400 nm by vector colorimetry. Quadratic function relationship was found between values of vector chromaticity and mass concentration of arsenic in the range of 0.020-0.200 mg·L^-1, with detection limit (3s/k) of 0.005 mg·L^-1. The detection reagents could be kept stable for 3 months. The determination results of arsenic in actual water samples obtained by this method were consistent with those obtained by ICP-AES. Values of recovery obtained by standard addition method were in the range of 99.8%-112%.