The performance of a cell averanging detector is researched under a narrowband stationary Guassian clutter background and chi-square target models. A general formula of detection probability and a recurrent algorithm which is convenient for calculation are derived. The results indicate that the false alarm probability rapidly decreased and the detection probability evidently decreased with the increase of signal-to-clutter ratio when the target signals present in reference cells

the fluctuating level of targets is different

and the performance of detector will be different either. Finally

a principal adaptive scheme decreasing target signals in reference cells which effect on the detection performance is presented.