Abstract: Analyzes the newly developed aspect-oriented programming approach and the disadvantages of object-oriented theory in defining XML document. Defining the XML document by aspect-oriented programming to extend it is proposed to solve the problems found in original definition, such as too simple relationship of inclusion, code redundancy, scattered crosscut concerns and having to modify original elements if extending XML elements. Introducing the concept of crosscut concerns and weaving them statically/dynamically into the definition of XML document enables the XML document to serve the function of aspect-oriented programming. So, the identification elements covering aspect, pointcut and advice are added to the original definition of XML Schema as defined ones, and some representative symbols are given to them correspondingly with mathematic descriptions. The results indicate that such a form of definition can reduce the system code redundancy and coupling degree of modules with better modularity and transportability grained.