The present invention belongs to the digital information transmission controlling technical field of an Ethernet switcher, in particular to a method for controlling the dual-port threshold queue sharing memory switching support multicast. The method uses the effective service quantity as the main basis for controlling each port queue threshold, to make sure that each port bears the same flow pressure, thereby to keep the system in a balanced state. Based on the classic effective bandwidth, and the imputed flow rate and the size of the distributed buffer area are combined together to define the effective service quantity of the output port, and to measure the flow pressure accurately. The application of the dual-port threshold not only enables the public memory space to keep the balance in the sense of the average, but also can realize the relieving in the sudden periods, and the forwarding of the cell of the multicast can also be integrated into the work framework. The simulation results show that in different flow modes, the method has greater improvement in the efficiency and the fairness than the traditional dynamic threshold algorithm.