This paper analyzes an influence of speed of the supersonic speed stealth aircraft on dynamic RCS series and radar detection performance. First of all, the paper sets flight tracks in accordance with aerodynamics, and obtains the real-time angles of radar sight with random jitter. Afterwards, the paper analyzes an influence of speed on dynamic RCS series by utilizing physical optics and method of equivalent currents. Finally, based on the stealth aircraft’s RCS fluctuating data, the paper deduces the computational formula of detection probability of fluctuating targets, and researches on an influence of speed on radar detection performance. The results show that the greater the speed is, the lower is the probability, and the more severe is the fluctuating detection. This research can provide a support for the detection of supersonic speed stealth target.