The Web Services Choreography Description Language (WS-CDL) is a newly developed specification for web services composition to describe the observable behav- ior across multiple participants from a global perspective. However, this specification does not provide a formal se- mantics, whose informal description can lead to ambigu- ous understanding and different implementations. Hence, it causes difficulties for the engineering community to an- alyze the business behavior and ensure the correctness. In this paper, we present the semantics of WS-CDL in terms of process algebra CSP which has great advantages in de- signing and verifying concurrent processes. Therefore, all the properties we want to check within a WS-CDL docu- ment can be verified automatically in the CSP framework correspondingly. In addition, the exception and compen- sation handling mechanism, an important concept of long running transactions, is demonstrated clearly through our formalization work.