The filter-fluorescer x-ray diagnostic (FFLEX) in the Shenguang (SG) laser facility has been upgraded to infer the time-resolved behavior of hot electrons in inertial confinement fusion experiments. It significantly increases the bandwidth and anti-interference ability requirements of readout electronics. The current readout method is difficult to meet these requirements. A dedicated front-end waveform digitizer (DFWD) for the FFLEX is presented in this paper. It is very convenient to be installed in the front-end detectors of the FFLEX, and so the DFWD could be shielded as well as detectors. The test results show that it works well in the front-end environment. Compared with the existing system, the DFWD can minimize the impact of radiation on signal measurement and significantly improve the accuracy of the status and time-trend diagnosis of hot electrons.