A context inference system including a mobile device and at least one information sending unit is provided. The mobile device includes an information receiving unit and a context operation platform. The information receiving unit receives a context information. The context operation platform includes an information collection module for collecting the information used for inferring a context based on a convergent search and an expanded search, a data classification and storage module for storing and classifying a user preference information of a user, and an inference module for inferring a context. The information sending unit transmits the context information to the mobile device. The context operation platform performs a context inference process according to the context information and the user preference information in order to forecast the user's need and provide a recommendation information to the user.