Mapping between Parlay Application Programming Interface (API) and network protocol is the keystone in the realization of Parlay-based services. This paper focused on Session Initiation Protocol (SIP), researched the mapping problem of Parlay and SIP, designed and realized the model of SIP message mapping in Parlay gateway, testified the mapping model by the testing environment. Testing results prove the mapping model has bidirectional mapping function between Parlay and SIP, as well as high feasibility and maneuverability.