Due to the problem of different QoS granularity in integrated UMTS/WLANs, how we construct effective QoS mapping mechanism for user satisfaction is essential during the changes of access networks, so called, handoffs. So in this paper, a novel dynamical QoS mapping mechanism based on Application Service Map (ASM) is proposed in order to support end to end QoS and minimize the service quality degradations. Based on the access network corresponding classification methods, all services can be categorized by priority and subdivides each grade of service into three sub-levels based on ASM. The proposed mechanism contains a two-way QoS mapping adjustment mechanism and it can dynamically adjust the QoS mapping relationship to optimize the allocation of resource according to present load condition of network. And a two-level QoS mapping selection algorithm based on the sub-level and priority of QoS service is used in the two-way QoS mapping adjustment mechanism to adaptively select more refined QoS. As an experimental result, the proposed mechanism can greatly improve the utilization of network resource and the user's satisfaction.