Frisch-ring CdZnTe detectors have demonstrated good energy resolution for identifying isotopes, <1% FWHM at 662 keV, and good efficiency for detecting gamma rays. To facilitate the application of this detector in radiation detection, we are designing a portable device that can incorporate with an 8times8 Frisch-ring detector array. A prototype system has been designed, which includes detector modules, front-end electronics, signal processing circuit, USB interface and high-voltage power supply. This paper describes the design and assembly of the detector modules and the structure of the prototype system. Some test results are also reported.