Green communication receives a growing number of concerns due to the consideration for energy and environment issues. On the other hand, the evolution of mobile and wireless communication also results in heterogeneous Radio Access Technologies (RATs), such as Wi-Fi, UMTS, LTE, CDMA2000 and so on. As a result, energy saving by inter-RAT cooperation has raised significant discussions in both industrial and academical worlds. In this paper, we concentrate on inter-RAT energy saving for multicast services. Moreover, we use Integer Linear Programming to model the problem and propose a distributed algorithm which can efficiently save the energy consumption.