The invention provides a multicast service protection construction method and device. The multicast service protection construction method comprises the following steps: determining a first data center corresponding to a first user node in an elastic data central optical network, and classifying the first user node into a first group; and dividing the first group into N sub-groups, constructing afirst primary sub-tree according to the first sub-groups and the first data center, and calculating a second path from the first user node to a second data center, so that the first path and the second path do not intersect. The multicast service protection construction method provided by the invention effectively overcomes the shortcomings that a traditional multicast service protection strategyis large in difficulty in calculating a light tree and high in resource occupation, and can effectively improve the use efficiency of frequency spectrum resources, reduce the time delay of a user to access to the data center, improve the blocking rate performance of the network, and improve the bearing capacity of the network on multicast services.