The radiation monitoring system for reactor coolant pressure boundary coolant leakage is one of the important radiation monitoring systems in nuclear power plant, and 18F has attracted the attention of many researchers because of its long half-life and the characteristic of positron–electron annihilation. In order to measure the detector signal accurately, the waveform digitization technology based on high-speed ADC is proposed. In this paper, the research background, waveform digitalization and the performance evaluation method of high-speed ADC is described firstly. Then the digital waveform measurement system is designed. Finally, the ADC dynamic performance and waveform digital measurement system are tested. The results show that the dynamic performance of high-speed ADC is basically close to the official manual, and the pulse waveform below 10 MHz can be reproduced perfectly. The technology proposed in this paper is is effective and universal, and it can be extended to other radiation monitoring subsystems in nuclear power plant.