The mixture of wheat straw (WS) and polyester (PC) was liquefied in supercritical ethanol. Liquefied products produced and liquefied residue from the liquefaction under different supercritical conditions were analyzed by GC-MS, SEM and IR. GC-MS analysis of the liquefied products indicates that ethanol would decompose. And the most compounds in the liquefied product had the structure of phenol and phenol derivatives, which came from the degradation products of PC and WS. SEM analysis show that the wheat straw powder possessed larger particles with smooth surfaces while the residue from liquefaction had smaller particles with rough surfaces because of drastically degraded from the wheat straw powder surface under supercritical conditions. FT-IR analysis showed that the lignin was easily degraded during the liquefaction process, and also found to the cellulose is very difficult to liquefy for its crystalline structure.