Nowadays the B/S (Browser/Server) architecture has be- come one of the most popular approaches to implement the web service. Because of the instability of the web environ- ment, keeping the consistency of the data is of essential im- portance. Consequently we turn to formal methods intend- ing to avoid inconsistencies in the B/S architecture. This paper describes a service-oriented system with the B/S ar- chitecture using the CSP (Communicating Sequential Pro- cesses) method. We define the processes in the system and the behaviors of them. After the definition, we analyze the causes of inconsistencies and demonstrate that the formal definition and mechanism we made can implement an in- consistency free system, which means the inconsistency can be avoided or fixed.