A method for resource admission control process, an Access-Resource and Admission Control Function entity and a Service-based Policy Decision Function entity, wherein the method includes: sending an Admission Request message, which carries the current media stream address information, to an Access-Resource and Admission Control Function entity (A-RACF) in an originating home network from a Service-based Policy Decision Function entity (SPDF) when the SPDF successfully configures an IP Multimedia Subsystem (IMS) connection for a Core Border Gateway Function entity (C-BGF) in the originating home network; and performing a resource admission control process for a corresponding media stream by the A-RACF according to the received Admission Request message. With the method of the present invention, the resource admission control process performed by the A-RACF on the media stream may become meaningful.