Abstract: 【Objective】 In order to investigate the effects of Adelphocoris lineolatus on the plant growth and nutritional quality of Medicago sativa. 【Methods】 The adults of A. lineolatus with different were inoculated to M. sativa plant. The plant height, branch number, stem-leaf ratio, dry weight, crude protein, ether extract and acid relative feeding value (RFV) were determined. 【Results】 The results showed that there was a significant negative correlation between A. lineolatus density and plant height (P<0.001), with the highest value in the control group (42.51 cm) and least value in 8 insects/cage (25.24 cm). With the increase of density, the stem-leaf ratio showed a significant upward trend (P<0.001) while the dry weight showed a significant downward trend (P=0.009). The crude protein (P=0.02) and ether extract content (P<0.001) also showed a significant downward trend. Meanwhile, A. lineolatus density significantly affected RFV (P<0.001), with the highest RFV (204.14) in the control group. Compared to the control, the RFVs in 1, 2, 4 and 8 insects/cage treatments were reduced by 0.56%,9.01%,21.85%,23.16%, respectively. 【Conclusion】 This study confirms that the damage of A. lineolatus reduces the yield and nutritional quality of M. sativa, and provides a basis for strengthening the control of A. lineolatus in the field.