An apparatus and method for preventing an acoustic shock of a portable terminal are disclosed. The apparatus includes a transceiver gain determining unit including a table of gain values for sound signals in each of one or more call modes, configured to output a particular gain value corresponding to a particular call mode; a reference value determining unit configured to receive the gain value from the transceiver gain determining unit, monitor a change in the gain value, and determine a predetermined reference energy value based on the change in the gain value; and an output level adjusting unit configured to receive an input signal, compare the input signal with the predetermined reference energy value, and adjust the level of the input signal to output an output signal.