Abstract: An ATM switch having the buffer threshold controller to control the cell input into the switching element using the back-pressure signal and a method for determining the buffer threshold according to the buffer threshold controller are disclosed. The ATM switch includes buffer pool storing the cell input to the switch; buffer pool control part storing the buffer pool occupancy information per input port of the buffer pool; threshold control part receiving the buffer pool occupancy information from the buffer pool control part and calculating the threshold per input port periodically and then sending it to the buffer pool control part; input crosspoint control part controlling the cells input to the buffer pool by receiving the control signal from the buffer pool control part; and output crosspoint control part controlling the cells output from the buffer pool by receiving the control signal from the buffer pool control part.