In optical multicast, because of the high cost and complex architecture of multicast capable (MC) node, splitter-sharing switch structure is introduced. To accommodate to this structure, a multicast routing algorithm in splitter-sharing optical network and a changing link weight policy to balance traffic throughput are proposed. At the same time, by extending RSVP and OSPF, an optical multicast protocol mechanism is provided. Simulations in NSFNET show when the number of splitters is 25% of that demanded by traditional MC nodes, the performance has been close to the ideal circumstance. Using changing link weight can improve the performance fairly but has a longer setup time.