To better assess field X-frequency band RCS dynamic tracking performance of measuring system and the quality of the RCS measurement data, based on the uncertainty analysis and principle of RCS measurement, in this article, the uncertainty influencing factors in the process of RCS measurement from the radar system, environmental factors, calibration system are analyzed, researched and established the system uncertainty source, and combined with the specific measuring conditions, the uncertainty of system is given, so can fully grasp the quality and accuracy of the measurement data, provides support for describing the results of the measuring system preferably. At the same time, the uncertainty analysis method in paper can be combined with other measurement conditions, has extensive universality and applicability.