Outdoor static RCS measurement is the principal means to obtain the RCS value of the full-scale targets. This paper firstly presented the imaging principles of the pulse-pulse stepped-frequency radar system. Based on the dominating characteristics of the outdoor RCS measurement, a wide-band (2-18 GHz) and two-channel RCS measurement system was designed and implemented in this paper, which could be applied to backscatter RCS measurement of the full-scale static target, and the high-resolution 2-D imaging of the scatter sources. It could provide the high-precision RCS data of target for the operational frequency range 2-18 GHz. Finally, the technical features of the instrumental radar system were also introduced in detail. This wideband RCS instrumental radar system has been successfully used in an outdoor RCS test range now.