IMS(IP Multimedia Subsystem) gives customers a rich multimedia experience. At the same time, it proposes a heigher demond about QoS(Quality of Service) management. Network operators will need to formulate different policy through service differentiation. Although 3GPP have defined Policy-based QoS management architectures, these architectures are only logical architectures and not physical implementations. This paper analyzes Policy-based QoS management model, proposes a implementation scheme which refers to 3GPP standards, designs and realizes Policy Decision Function and Pocicy enforcement Function which are key servers in the model. Upon testing, this service model can correctly complete the subscriptions of policy information, policy decision, bandwidth requirement, QoS class consultations and provide reference to Network operators.