The invention provides a compound enzyme for producing reducing sugar by degrading maize straws. The compound enzyme is prepared from pectase, cellulose, hemicellulase, ligninolytic enzyme, amylase, prolease, lipase and chitosanase. Compared with the prior art, 1) the yield of the reducing sugar by degrading the maize straws has high yield, and the gross amount of the reducing sugar of straws pergram reaches over 480 mg, so the compound enzyme has wide application prospect in the fuel alcohol industry; 2) compared with sugar preparation by acid process, severe acid pollution is prevented to facilitate subsequent fermentation; and 3) compared with monomer cellulose or simple compound enzyme, the pretreatment of steam explosion with high energy consumption is not required, and the amount of the reducing sugar is increased by over 1 time; meanwhile, glucose and xylose in a degradation product have high content, side products are few so as to contribute to subsequent fermentation, the industrial application value of the maize straws is improved, and the compound enzyme can be applied to production of single cell protein and fuel alcohol.