Abstract: When performing RCS measurements for outdoor targets, usually the whole space range under measurement is greatly longer than the actual target zone, which causes very large data storage and makes further data processing difficulty. To solve this problem, an effective method is presented in this paper, which can largely reduce measurement data. In this method, a related local oscillation signal is generated to be mixed with the received signal, which can greatly decrease the carrier frequency of the return signal from targets. With this method, a much lower sampling rate is guaranteed, which can greatly reduce the data storage and signal processing time.