This paper reports the result of computer simulation about compound action potential of a sural nerve with and without fiber loss. A compound action potential is a wave of electric potential detectable on the skin after electric stimulation of a peripheral nerve. The loss of nerve fibers, which is observed in some neuropathies, is considered as the cause of low amplitude and slow conduction of the wave. To quantify the relationship between fiber loss and compound action potential, computer simulation of the stimulation of a human sural nerve was executed. As a result, the conduction velocity of the first negative peak of the compound action potential was substantially reduced in case of thick fiber loss, and was slightly enlarged in case of thin fiber loss. However the amplitude of the peak was not always reduced. The effect of thin fiber loss was observed in the amplitude of the second positive peak and the second negative peak.