This paper proposes a cognitive radio frequency (RF) stealth radar using phased array (PA) for surveillance applications. Since the traditional surveillance systems are accessible by intercept receivers, the series of low-gain beam is used to reduce the visibility of this system. The traditional high-gain PA antenna beam is replaced by the novel beam. And the original detection performance isnot degraded. Furthermore, we combine cognitive radar with these low-gain beam to update current operation parameters, the update scheme of closed-loop adaptively is denoted to real-time update this weighting vector for aiming to the target and compensating the Doppler shifter. Through the simulation results, this paper confirms all the methods these were proposed.