For reducing the network coding cost in optical field and improving the probability of realizing optical multicast theoretical maximum capacity in optical multicast routing, a multicast method based on shared links and network coding is proposed to optimize the optical multicast capacity in this paper.In the proposed method,a strategy is designed firstly to choose t he multiple shortest path s from source node to each destination node,respectively . These shortest paths make up the shorte st path cluster for the multicast . Then, the link shared degree of each path is calculated in the shortest path cluster. T he paths with high link shared degree are selected to transmit the encoded multicast information .The multicast sub - graph is construc ted by the link needing few est number of network coding operations to optimize network coding cost .The proposed method can solve two routing problems:one is too many times of network coding operations in the traditional network coding multicast routing,an d the other is too low probability of reach multicast maximal capacity for the multicast routing based on maximal shared degree links.Compared with the above two multicast routing methods,the simulation results show that the proposed multicast routing metho d can get the lowest network coding cost, the maximum probability of achieving optical multicast theoretical maximum capacity and appropriate multicast average routing cost.