Root exudates of plants under saline-alkali stress contain abundant biochemical information and play an important ecological role. In order to explore the composition of root secretions of salt-tolerant pasture grass Echinochloa frumentacea under salt-alkali stress, and to reveal its physiological and ecological functions under salt-alkali stress. A hydroponic experiment was carried out on Echinochloa frumentacea in an artificial climate chamber, with neutral salt (NaCl+Na₂SO₄ 100 mmol/L), alkaline salt (NaCl+NaHCO₃ 100 mmol/L) and alkali (Na₂CO₃+NaHCO₃ 50 mmol/L) treatments at the seedling stage. After 3 days of treatment, the composition of compound of root exudates in the control and treatment groups was detected by LC-MS/MS. The results showed that there were 334 compounds in root exudates of Echinochloa frumentacea under salt-alkali stress. According to the VIP score of OPLS-DA and the P value of t-test, 22, 15 and 21 differential root exudates were found for control-vs-saso100, control-vs-soda50 and control-vs-salt100, respectively. The compositions of root exudates under alkaline salt and alkali treatments were similar, including lipids, phenolic acids, alkaloids, phthalides, amino sugars, terpenoids, quinones, amino acids and their derivatives; There are lipids, phenolic acids, alkaloids, phthalides, terpenoids under neutral salt treatment. KEGG annotation and enrichment showed that root exudates under saline-alkali stress not only contained carbohydrates, nucleotides, amino acids, fatty acids, lipids and vitamins produced by tricarboxylic acid cycle metabolism, but also were related to Warburg effect, membrane transport, signal transduction and genetic information processing. Studies have shown that Echinochloa frumentacea improved its adaptability to saline-alkali stress through exudation of root exudates, regulating its metabolite concentration, enhancing or changing carbon assimilation, respiration, and signal transduction.