A method for easing data transmission congestion in a switch device having a plurality of ports. The switch device includes a shared buffer capable of dividing into a plurality of buffering units. The method comprises the steps as follows. A plurality of output queues are provided, in which the output queues have a one-to-one correspondence with the ports, and each output queue has a number of reserved buffering units. The buffering unit(s) are then assigned in the shared buffer. A packet is received from a source port and storing the packet in an assigned buffering unit. The target port of a packet is determined according to a header of the packet. Then, the buffering unit containing the packet is linked to the output queue that corresponds to the target port. The free buffering units are thus controlled according to a number of reserved buffering units in the output queue and a triggering or a terminating condition of the source port.