This paper designs Rich Internet Application (RIA) system integration that combines Flex and Web services. Application systems business processes are encapsulated by standard Web services. Discovery and sharing of enterprise data resources can be achieved by using the publishing and discovering mechanism of services. Transmission messages are digital signatures and encryptions by using the encryption algorithm. The unified rich client user interface and high interactivity and response of the client and rich user experience are provided by using Flex. System performance, which are improved by using modules, navigation, components of dynamic load, and components of reuse. Feasibility and rationality of the built RIA integration are verified using Flex and Web services combined with the J2EE.