Abstract: The structural layer of crude fiber in the roughage of cereal was investigated by enzymatic hydrolysis. The crude fiber consists of two layers, i.e., the free type of cellulose and hemicellulose, it was easy to be hydrolyzed by enzyme; and the combined type of cellulose and hemicellulose bonded to lignin, it was hard to be hydrolyzed by enzyme. It was found that the former was hydrolyzed by enzyme containing 80.98% of the total hemicellulose and containing 19.31% of the total cellulose in cotton stalk. The former was hydrolyzed by enzyme containing 60.23% of the total hemicellulose and containing 44.36% of the total cellulose in maize stalk. The former was hydrolyzed by enzyme containing 46.20% of the total hemicellulose and containing 43.04% of the total cellulose in wheat stalk. The former was hydrolyzed by enzyme containing 47.60% of the total hemicellulose and containing 51.80% of the total cellulose in rice stalk. It suggests that this could be the main reason for lower ratio of digestibility and metabolism of roughage.