In order to adapt to the changes in software development mode of water resources information system, on the basis of .Net platform and with an object-oriented approach, a study on middleware application technology has been carried out taking the “Water Resources Information Management System” as example, involving “data entry middleware”, “data editing middleware”, “data retrieval and statistic middleware ”, “user security middleware” and “data communication middleware”, etc. The middleware modules can be used for multi-platform, with good reusability and security.