Performance of a radar system is usually degraded by some undesired variations in the environment. Hence, for overcoming these degradations, flexible detectors should be used to adapt to these variations. Based on this fact, detection and estimation theory are important in designing the adaptive detectors, and many adaptive detectors have been proposed using this theoretical approach. In many cases, some specific models are assumed for the target and interference. It is clear that the closer this model matches the real conditions, the better performance would be obtained in a radar system. In this thesis, based on detection theoretic approach and using proper models for interference and target, an adaptive detector is proposed. In this detector, target fluctuation is considered and by computer simulation it is shown that it has better performance in comparison with the other detectors. On the other hand, because the radar detectors are designed with the assumptions for target and interference, the compatibility of these assumptions with read conditions should be investigated. Therefore, by simulation of the radar environment including sea, land and atmosphere clutters, the performance of several adaptive detectors are investigated and some suitable practical results are presented.