Most of IoT applications include large number of distributed sensors which are interesting in specific geographical area. A large number of IoT entities have multiple relations and dynamic connections with each other. And there are many group communication requirements. Flexible multicast mechanism will be essential in such environments but it is difficult to satisfy verious requirements by means of the legacy multicast mechanisms. Therefore, we propose a novel software defined network multicast mechanism based on group shared tree, and a flexible group management for dynamic multicast services. Finally, we prove the functionalities and performance of the proposed SDN multicast mechanism.