<p>With the rapid development of space technology and the increasing demand for global security early warning, space-based early warning Radar (SBR) is playing an increasingly important role in defending against potential threats. Based on the perturbed motion model of low-earth orbit satellites, this paper proposes a method for calculating the beam grazing angle of SBR using coordinate transformation techniques. The method is characterized by its clear process and simple calculation. The effectiveness of this method has been verified through simulation experiments, providing a practical method for the real-time calculation of the beam grazing angle of SBR.</p>