A method and system for dynamic consulting QoS in NGN. In present invention, RACS (The Resource andAdmiss ion Control Subsystem) has a interface for communicating with transmitting function module, service controlling function module and NASS (The Network Attachment Subsystem) so that when the NGN user terminal develop a service that needs QoS ensure, RACS can obtain the Qos requirement parameters of the service, and determine the Admission Control parameters based on said QoS requirement parameters; Finally, the determined Admission Control parameters are transmitted to transmitting function module, the QoS ensure for said service is achieved. The present invention can perform Qos consulting process of end to end according to resource usability of the current network, thereby the usability of QoS consulting process result is enhanced effectively. Therefore, the present invention can effectively ensure QoS of service transmission in NGN.