With the development of multicast applications,the reliable transmission of multicast services over optical layer becomes a hot topic in today's research on optical networks. The key problem of this topic is multicast protection algorithm,which is discussed only in optical network with full multicast ability.However,due to cost consideration,the real-life optical networks are actually sparse multicast network with only a few multicast capable nodes. To deal with this situation,a virtual source-based dynamic multicast protection algorithm is proposed. The simulation results show that this algorithm can achieve better resource efficiency and lower time complexity.