The recent advance in structure-function studies of cellulases by structural biology and protein engineering is reviewed.The seperation of structural domains and the structure-function studies of catalytic domains and cellulose-binding domains are included.The research prospects of cellulases are forecasted.According to the sequence similarity of amino acid, cellulase and hemicellulase can be divided in to nine families, and in five families there are some enzymes that three dimension structure have been resolved.Here, three dimension structure of some cellulase and xylanase were compared, and the relationship between its molecular folding and catalytic mechanism were also analyzed.