The aim of this study was to investigate the effect of micronization on the physicochemical properties of corn stover. With the decrease of powders in four different particle sizes, the bulk density changed from 0.11g/mL to 0.41g/mL, the surface area increased to 1.05m2/g, and the angle of repose and slide of corn straw powder increased to varied degrees. Changes of the microstructure and physicochemical characteristics of different powders were assessed by using scanning electron microscopy and X-ray diffractometry. Compared to general powders, with the agglomerates in ultrafine grinding powder and increased size distributions, the ultrafine grinding reduced the particle size and crystallinity of the wheat straw significantly, that means the ultrafine powder diameter was reduced to 15.54μm, and the crystallinity was reduced from 44.72% to 13.68%. Both of the microwave-assisted and general oil bath heating were carried out in alcolhol liquefaction. With the microwave heating, the liquefied yield of ultrafine powder was 90.37% within 5min, however it needed around 1h with oil bath heating, which indicated the effectivity of microwaves. With the general oil bath heating, the liquefied yield of ultrafine powder was 95.30% with in 120min, which was higher than that of common powder (＜025mm). The results showed that ultrafine grinding technology could increase the liquefaction extent and rate. In addition, ultrafine grinding could impove liquefied yield by reducing the particle size and crystallinity of the corn stover.