E-learning is being increasingly viewed as an important activity in the field of distance and continuing education. Web-based courses offer obvious advantages for learners by making access to educational resources very fast, real-time and relevant, at any time or place. With the rapid development of network, the resources of E-learning systems get richer and richer. However, the rapid development of the networks makes the existing network technology face challenges of all sorts too, and there is no exception in E-learning systems. XML is referred to "Secondgeneration of Web language" by the features of its own scalability, openness and interoperability. XML enjoys obvious advantages in E-learning systems by providing the data description language which is cross-platform and cross-network, and it can also divide data from data structure and provide more precise and meaningful search. This paper focuses on the information expression technology based on XML in E-learning systems. In addition, a three-tier model based on XML and the process to achieve is described.