Non-Rayleigh clutter statistics result when sea or ground clutter are viewed with resolution radars (pulse width <0.5 mus) at low grazing angle (phi<5 degrees). In this paper, we consider the problem of Clutter Map Constant False Alarm Rate detection (CMAP-CFAR) in Weibull distribution with a shape parameter known. The target is assumed to be fluctuating according to Swerling I model. Closed form expressions for the probabilities of detection and false alarm in terms of shape and scale parameters arc determined and the performance of the system is investigated and analyzed.