Abstract: A pot experimental study on the effect of Spraying Selenium (0, 0.1, 0.2, 0.4, 0.8 mg.L-1) on the nutritional quality and flavor of lettuce leaf. The results showed that foliar application of selenium increased the content of sweet amino acids, umami amino acids and bitter amino acids of leaf lettuce, and it reached peak when Se was 0.2 mg.L-1. The content of organic acid, citric acid, malic acid and tartaric acid were increased in different degree by Spraying Selenium on the leaves. At 0.2 mg.L-1 Se, the total acid content, citric acid content, malic acid content and tartaric acid content reached the maximum value. At 0.8 mg.L-1 Se, the total flavor substances in leaf lettuce increased by 44.15%. The content of 2-octanol, 4-hydroxy-4-methyl cyclohexanone, 7-pyrrolidone and hexyl acetate increased by 32.31%, 28.87%, 33.46% and 80.52% compared with the control, respectively. Foliar application of selenium improved the nutritional quality of lettuce and increased the content of flavor substances, and the best treatment was 0.2 mg.L-1 Se.