【Objective】 Polyploid breeding has widely been used in the genetic improvement of different tree species because of the rapid and extensive growth of polyploid plants. There are many studies describing polyploidy in Populus hybrids, but most of them focused on growth traits, wood properties and stress tolerance, and few studied their growth and development mechanisms. In this study, the salt tolerance mechanisms of polyploid were deeply studied through proteomics analysis, and their metabolic regulation mechanisms were revealed, which could provide a theoretical reference for their high yield breeding. We studied salt tolerance mechanisms of triploid Populus hybrids, which was of great significance for improving salt-tolerance of P. simonii × P. nigra. 【Method】 In this study, we used triploidP. simonii × P. nigra hybrid clones which were treated with 75 mmol/L NaCl solution for 0, 4, 8, 12 and 16 days, and we analyzed the differentially expressed proteins from leaves by two-dimensional electrophoresis and MALDI-TOF/TOF mass spectrometry under salt stress in different treatment conditions. 【Result】 More than 4 000 protein spots were detected in this study. There were 96 protein spots showing different expression patterns after the treatment. We identified 5, 21, 36 and 34 differentially expressed protein spots under salt stress on the 4th, 8th, 12th and 16th day, respectively, compared with the control group. The up-regulated proteins were 1, 7, 17 and 9, respectively, while the rest were down-regulated proteins. Sixty proteins were successfully identified by mass spectrometry. These proteins could be divided into eight categories according to their functions, and 15 photosynthesis-related proteins, including phosphoribulokinase and photosystem Ⅱ oxygen-evolving complex protein two precursor, accounted for 25% of the total protein content. There were 12 energy metabolism-related proteins, including triosephosphate isomerase and fructose-bisphosphate aldolase 1, which accounted for 20% of the total protein content. SOD, glyoxalase I homolog family protein, and seven other redox-related proteins accounted for 12% of the total protein content. H⁺-transporting two-sector ATPase family of proteins and five other resistant proteins accounted for 8% of the total protein content. Four biosynthesis and metabolism proteins, including S-adenosylmethionine synthase 3, accounted for 7% of the total protein content. Two transport proteins accounted for 3% of the total protein content, one belonging to the MD-2-related lipid recognition domain-containing family of proteins, and the other being a temperature-induced lipocalin. The signal transduction protein only contained thylakoid lumeinal 29 ku protein and accounted for 2% of the total protein content, and 14 unknown proteins accounted for 23% of the total protein content. 【Conclusion】 Under salt stress, multiple proteins (mainly photosynthesis and energy metabolism related proteins) were co-involved in the response to salt stress. This study can provide a basis for future studies of tree proteomics under salt stress.