Application-layer multicast (ALM) can solve most of the problems of IP-based multicast. Topology-aware approach of ALM is more attractive because it exploits underlying network topology data to construct multicast overlay networks. In this paper, a novel mechanism of overlay construction called Multi-domain Topology-Aware Grouping (MTAG) is introduced. MTAG manages nodes in the same domain by a special node named domain manager. It can save the time used to discover topology information and execute the path matching algorithm if there are some multicast members in the same domain. The mechanism can lower the depth of the multicast tree too. Simulation results show that nodes can acquire multicast service more quickly when the group size is large or the percentage of subnet nodes is high.