In view of the fact that the multiple constrained QoS multicast routing is a NP-Complete problem, a controllable strategy for decomposing and composing multicast tree is introduced. Different trees of little cost will be gained under the strategy, so that the problem of local best can be solved effectively. An ant colony algorithm, which divides the ant colony into ant assembly according to the ends of multicast, is designed on the basis of the strategy. The pheromone updating mechanism is improved with the “dead-point” punishment and the encouragement and punishment to the multicast tree strategy, so that the algorithm can converge fast. Simulation results demonstrate that the method can solve the QoS multicast routing problem effectively, and perform well as the size of network increases.