This paper deals with the structure variation of wheat straw alkali lignin in alkaline ionic liquid ［Bmim］ ［OH］and the dissolution mechanism of alkali lignin． The dissolution was assisted by microwave heating with a microwave power of 500 W，a temperature of 90 ℃，a reaction period of 30 min and a solid-to-liquid ratio of 1∶10． By using ［Bmim］ ［OH］ionic liquid as a solvent，the lignin dissolution process was characterized and analyzed by means of FT-IR，GPC，elemental analysis，2D HSQC NMR and Py-GC-MS． The results indicate that，during the dissolution of alkali lignin in ionic liquid ［Bmim］［OH］，the aromatic rings remains stable and there mainly occurs the substitution of the side chain or the removal of oxygen-containing groups; and that，after the dissolution，the relative molecular mass of the regenerated lignin slightly decreases，the molecular mass distribution become more uniform and the degree of unsaturation increases due to the dehydration reaction during the dissolution processes． Moreover，2D HSQC NMR and Py-GC-MS results prove that there mainly happens the cleavage of β-O-4' aryl ether linkages during the dissolution of lignin in strongly basic ionic liquid system，followed by β-β and β-5 structures，and the S /G ratio remarkably decreases． This research provides basic data and an approach to the development of relevant theories and the application of high-value alkali lignin