Grains stillage， rich in cellulose and hemicellulose， is a favorable resource of raw materials for the preparation of microcrystalline cellulose （MCC）. In order to make full use of the cellulose components in grains stillage， the preparation parameters of high purity MCC from grains distillers （GSMCC） were investigated based on acid hydrolysis method， followed by the extraction of crude fibers by nitric acid-ethanol method， and the structural characterization during isolation of GSMCC were determined. The technological parameters， such as hydrochloric acid concentration， temperature， liquid-solid ratio and hydrolysis time， were optimized by response surface method with the index of purity and yield. The results showed that the optimal preparation conditions of GSMCC were as follows： time of 2 h， temperature of 72.3 ℃， hydrochloric acid mass fraction of 7.5% and liquid-solid ratio of 25 ∶ 1（mL/g）. Under the optimal conditions， the yield， purity and degree of polymerization （DP） were 89.25%， 92.57% and 276.39， respectively. The purity of GSMCC was increased to 93.31% after bleaching， and the degree of polymerization was reduced to 255.86. The results of structure characterization by using SEM， FTIR and XRD showed that the microstructure of GSMCC is irregular granular type， which has a typical functional group of cellulose with characteristics of cellulose Ⅰ crystal. The degree of crystallinity is 67.49%. TGA shows that the heat stability of GSMCC is nice， indicating that the preparation of food additive microcrystalline cellulose from grains stillage is feasible.