Abstract: Quantum radar is a new concept radar that uses quantum resources to improve detection performance. It is an upgrade and improvement of classical radar. It is quite different from traditional radar in signal modulation, transmission, reception and detection. Based on the theory of quantum physics, in this paper the general formula of signal and noise of quantum radar is proposed,the general method and performance limit of quantum radar signal detection are studied, the general equation of quantum radar is proposed, and the equation of quantum radar in combination with the application of single photon detection radar is explained.The improvement of detection range of quantum radar compared with classical radar is analyzed quantitatively. At the end of this paper, the quantum radar equation and detection mechanism are summarized.