Abstract: Under the new service-oriented grid computing architecture,grid services offer a prominent paradigm for distributed computing on the Internet．It is an emerging opportunity for both service providers and service consumers to create the value-added service by assembling new,value-added grid service out of existing ones．grid services composition has become an important research issue in Grid field．As the complexity of the available Grid services,many of them exhibit complex session protocols,requiring that the offered operations are invoked according to specific rules．This paper addressed the problems:(1) how to specify complex session protocols of grid service,(2) how to construct composition rules to composite component service,and (3) how to verify grid services composition,especially its conformance to component services’ session protocols．Petri net provides the constructions for specifying synchronization of concurrent processes,and the programming language provides the constructions for specifying and manipulating data values,while colored Petri net (CPN for short) combines the strengths of Petri net with the expressive power of high-level programming language．In order to address the above problems,we proposed a CPN-based model for the specification of both the session protocol and the composition of grid services．Through using the colored token of CPN to model diffe-rent message and event type of business process,we can transform services session protocols and grid service composition process into CPN,then analyze and evaluate behavioral properties and performance of the system by CPN Tool,an available specific tool for CPN.

Key words: Grid service composition,Component service,Session protocol,Process combination,Colored Petri nets