How to maintain the false-alarm-rate constant of radar detecting system is one of the important problems in modern radar technology and signal processing technology. In order to obtain constant-false-alarm-rate in the complex clutter surrounding，radar detecting system must have a constant-false-alarm-rate processor (CFAR Processor). The AC-CFAR processor discussed in this paper is a new processor. Its CFAR threshold is implemented by selecting a mean value which approaches the detected distance-cell value. On the basis of simple hardware-implement，the AC-CFAR processor has an adaptive performance which can timely reflect the changes of external clutter，and a very good perfermance of anti-multitarget effect and antic1utter edge effect as well. It can also resist the effect ofb“ig target eat small target” and reduce CFAR loss.