Based on a thorough analysis and comparison of several business activity monitoring(BAM) system models, noting that a BAM system is open, integrative, and real-time, and using the SOA software engineering techniques, this paper presents a service-oriented dual-bus BAM system model and analyzes in detail the functions of its service components and communications among them. Much more open than prior models, this BAM system model has a two-level bus architecture, which enables flexible and extensible implementations of practical systems, as well as provides a foundation for software reuse.