To investigate the effect of arsenic on the growth of millet seedlings and the critical concentration of millet stress, the As concentrations were set to 0, 2, 4, 8, 10 mg/kg for quartz sand. Substrates, through cultivation and pot experiments, analyzed the effect mechanism of As on the germination, seedling growth and antioxidant enzyme system of millet. Studies have shown that:Low concentrations of As (<4 mg/kg) can promote millet germination, high concentrations of As (<4 mg/kg) inhibit millet germination, when the As concentration of 2 mg/kg, the millet germination potential, germination rate and germination index in all treatments the highest value. They were 18.67%, 32.00%, and 19.00%, respectively. The low concentration of As promoted the growth of millet seedlings, and the high concentration had an inhibitory effect. When the As concentration was 2 mg/kg, the plant height, root length, fresh shoot weight, and under ground fresh weight of millet were all reached. The maximum values were 15.46 cm, 7.34 cm, 0.64 g, and 0.16 g, respectively. As the concentration gradient of As increased, the fresh weight of the under ground layer increased first and then decreased, and the promotion and inhibition of the root system was greater than that of the shoot. The content of As in the roots of millet seedlings was significantly higher than in the shoots, and the TF value gradually dccreased. When As concentration was less than 4 mg/kg, As could promote the synthesis of chlorophyll in millet. When As concentration was 2 mg/kg, the total amount of chlorophyll a, chlorophyll b and chlorophyll in millet was significantly higher than that of the control 28.38%, 51.60% and 37.06%, when the concentration of As was higher than 4 mg/kg, the chlorophyll synthesis of Millet was inhibited; with the increase of As concentration gradient, the SOD activity of millet seedlings continued to increase, and the activities of POD and CAT increased first and then decreased, but higher than the contro. When the As concentration exceeded 8 mg/kg, the POD activity of the millet seedlings began to decrease. After the As concentration exceeded 4 mg/kg, the CAT activity began to decrease. After As concentration higher than 8 mg/kg, the POD actibvity of millet seedlings began to decrease. The results showed that low concentration of As (<4 mg/kg) promoted the germination and seedling growth of millet, and the high concentration of As(≥ 4 mg/kg) inhibited the germination and seedling growth of millet, and the root system was more sensitive to As stress, and the activity of antioxidant enzyme system (POD, CAT) was reduced. The research can provide a scientific basis for the anti-pollution cultivation and pollution-free production of millet.