The self-tracking system of digital phased array antenna has tracking error due to discretization because of the digital tracking loop. Aiming at the characteristics of self-tracking of digital phased antenna, a method is proposed to improve the real-time tracking of digital beam by using the inertia of self-tracking beam and interpolation. The experimental results show that the standard deviation of self-tracking discrete error is 0.086 6 without interpolation, while the standard deviation of self-tracking discrete error is 0.001 735 after interpolation, which reduces the discretization error caused by digital tracking loop when tracking high dynamic target.