Abstract: Aiming at the requirement for cosmic ray detection in Imaging Atmospheric Cherenkov Telescopes(IACT) using silicon photomultiplier(SiPM) detectors, a prototype of readout electronics is designed based on waveform digitization using the Switched Capacitor Array(SCA) ASIC. The prototype is able to read out SiPM detector signals with a wide dynamic range and then calculate the time and charge information of the input signal. The design scheme and structure of the readout electronics prototype are presented in this paper, and a series of tests are conducted to verify its performance. The preliminary results show that the time resolution of the readout system prototype is better than 800 ps RMS within the full dynamic range. The charge resolution is better than 30% at 5 P.E. and is better than 3% at 8 000 P.E.. The test results indicate that the readout system prototype meets the design requirements.