Abstract: The multicast network is one of the important and challenging problems that must be effectively resolved before multicast applications can be fully deployed on the Internet. Most existing multicast schemes focus on source based multicast trees. They either cannot be directly deployed in core based multicast trees or may render sub-optimal performance when directly deployed. Core based multicast selects a core node in the network, and then uses it to establish a single sharing tree covering all multicast group members, other than building trees for each source node, and so that it can save bandwidth enormously and enhance the data transmission efficiency. In core based multicast, core nodes in different positions will bring on different multicast trees, so the core node actually determines the performance of core based multicast. Therefore, core selection and migration are two important issues in core based multicast. In allusion to all-to-all multicast model, a complete core selection algorithm targeting at total cost optimization is given and the algorithm has low complexity; then two approximate algorithms are designed for real-time application and the analysis of approximation ratio is given; finally a scalable core migration algorithm is designed and the tree cost estimation mechanism in this algorithm provides a credible criterion for the migration time.