1. A resource and admission control method comprising: 501 ) a service control function (SCF) generating a resource initialization request; 502 ) the SCF determining Quality of Service (QoS) requirement parameters of services to be requested by a user, and then sending the resource initialization request to a policy decision functional entity of a home operator or retail service provider (PD-FE(H)); 503 ) after receiving the resource initialization request for requesting QoS resources for services, sent by the SCF, the PD-FE(H) making an initial policy decision for this resource initialization request to generate an initial decision policy; 504 ) the PD-FE(H) sending the resource initialization request to a PD-FE of a visit operator or wholesale service provider (PD-FE(V)) because the PD-FE(H) does not have requested transport layer resources; 505 ) the PD-FE(V) inspecting for authorization the resource initialization request, which includes verifying whether the requested QoS resources are consistent with local operator policy rules; 506 ) the PD-FE(V) deciding an access network and a core network which the requested QoS resources are involved with, and then sending the resource initialization request to a transport resource enforcement functional entity of the visit operator or wholesale service provider (TRC-FE(V)) based on a decision result to inspect resource availability of the involved network; 507 ) the PD-FE(V) making a final admission decision based on the authorization check result in step 505 ) and the check result of the resource availability in step 506 ) to generate a final decision policy, and then sending a resource initialization response to the PD-FE(H); 508 ) the PD-FE(V) sending the resource initialization request to a policy enforcement functional entity of the visit operator or wholesale service provider (PE-FE(V)) to install the final decision policy; 509 ) the PE-FE(V) installing the final decision policy from the PD-FE(V) and sending a resource initialization response to the PD-FE(V); 510 ) the PD-FE(V) sending the resource initialization response to the PD-FE(H); 511 ) after receiving the resource initialization response returned by the PD-FE(V), the PD-FE(H) deciding whether the initial decision policy is required to be installed in a PE-FE of the home operator or retail service provider (PE-FE(H)) for the resource initialization request, and then sending the resource initialization request to the PE-FE(H) to install the initial decision policy if yes; 512 ) the PE-FE(H) installing the initial decision policy from the PD-FE(H), and sending the resource initialization response to the PD-FE(H) after installing the initial decision policy; and 513 ) the PD-FE(H) sending the resource initialization response to the SCF; wherein the steps 508 and 509 are optional.