The invention discloses a method for determining the arsenic content of plants. The detection process of the method comprises the following steps: weighing 0.5g of plant sample sieved by 100 meshes, putting into a 50mL glass colorimetric tube with scales and a stopper, adding 35mL of concentrated nitric acid HNO, capping and immersing for the night, and meanwhile doing a reagent blank without samples; the next day, heating and digestion for 2 hours with a water bath at 100 DGE C; after heating and digestion are finished, putting a Vapor Block, and evaporating nitric acid to be dry at 120-130 DEG C; after catching acid is finished, taking down the colorimetric tube, cooling, adding 5mL of hydrochloric acid and 5mL of mixed liquid of 50g / L thiourea and 50g / L ascorbic acid, and adding ultrapure water to cause the constant volume to be 25mL; and after filtering, using an atomic fluorescence analyzer to determine the arsenic content. Compared with the traditional method for determining the arsenic content, the method has the beneficial effects that the advantages are significant, and the detection speed is high; the plant samples can be processed in batches, the practicality of nitric acid is greatly reduced, less nitrogen oxide waste gas is generated, and the environmental pollution is greatly reduced; and the detection result of the method has high accuracy and good repeatability.