In order to quantify background clutter reasonably, some collected images had been evaluated by using three metrics of background clutter. The metrics consisted of the probability-of-edge, the statistical-variance and the phase–correlation. The performance of these metrics was verified with the statistical results of target acquisition. It is demonstrated that the metric of probability-of-edge is more stable than others. Moreover, the fluctuation of the gray value in the image has a great effect on the performance of statistical-variance metric and it is not suitable to quantify the background clutter for the scene in which the mean of statistical variance of the background does not consist with the saliency of the target. And the homogeneous background has a great influence on the performance of phase-correlation metric and it is more suitable to quantify the background clutter for the scene in which much more information is contained.