In this study, a two-stage peak detection circuit was designed to realize the peak detection and holding of a narrow pulse signal with a rising edge of 3ns, pulse width of 5ns,falling edge of 3ns, and re-frequency of 10kHz. The voltage-signal acquisition was accomplished using the analog-to-digital converter of an STM32 microcontroller. The basic structure of the ground detector with an APD as the photodetector is given in the block diagram, where the amplifier circuit module in the detector system is used to increase the width of the received laser pulse from 1ns to 5ns. The peak detection circuit module is used to detect and record the data of the narrow pulse. The signal source was used to complete a functional test of the peak detection circuit, and a laser with a heavy frequency of 1kHz and pulse width of approximately 1ns was used to test the whole detector system. The results verified that this system could better detect and record the peak of this laser signal.