A method and system for automatic service composition is disclosed, wherein a service registry stores a plurality of service specifications received from at least one service provider in a service repository, and receives service requests from service requestors. A composition engine of the service registry can automatically generate a series of actions from service specifications stored in the service repository according to the service request, and then passes those actions to the service requestor for being processed. In order to facilitate the preceding procedure of automatic composition, the composition engine pre-processes service requests and service specifications, and declares suitable new objects. The composition engine also post-processes the planning resolution generated by the planning module for translating the format of the planning resolution into a processing language, and finally passes the resolution to a processing engine of the service requestor for being processed.