The invention discloses a testing system and method for directed dynamic tracking of a spacecraft mobile beam antenna. A target direction is regarded as an invariant, a spacecraft is about to be in superposed posture motion, and antenna motion is motion of an antenna tracking target output by a real spacecraft dynamics computer, so that the target direction becomes a fixed direction in a testing site, and pointing of the antenna mounted on a three-axis turntable is maintained in the target direction when the three-axis turntable rotates. Therefore, the system does not need an outside site or a compact site and is low in requirements on the site, high in testing accuracy and testing efficiency. The three-axis turntable is driven by data generated by the spacecraft dynamics computer, and antenna pointing is driven by data generated by measured corner of the three-axis turntable, which is consistent with an algorithm that the spacecraft adopts measured posture angle to calculate antenna pointing, so that verification of directed dynamic tracking is real, and the requirements on the site can be lowered.