Abstract: To avoid the lost or error phenomena caused by the analog-to-digital converter(ADC) conversion rate in the case of random input signals with pulse width and peak in the traditional discriminator,a CMOS peak-discriminator used in a nuclear pulse peak detector(PKD) was designed by using the differential zero-crossing comparator(DZC) to trigger the ADC to transform the peak-voltage into digital at the peak-time and trigger the circuit to reset PKD at the valley-time.The simulation results by Hspice show that the peak discriminator makes the peak detection system complete the accurate peak detection of all input signal,eliminate the restriction of ADC on conversion rate and reduce the dead time of the system.