Although Application-level multicast is a new multi-point data transmission model, there is no mature and effective scheme for network heterogeneity problem. This paper proposes an agent-based adaptive media multicast system, i.e., the so-called iPALM system (Proxy based Application-level Multicast). It uses efficiently data transmission of IP multicast in LAN, and every IP multicast area sets one agent server named MPN, the backbone network composed of MPNs transmits data using application-level multicast. At the same time, iPALM provides the head format of system protocol, and the definition of transmission message in XML format which demonstrates that iPALM system can satisfy every different application requirement, and improves the media service quality in heterogeneous environment.