The secant compensation must be applied in the servo system of the azimuth axis for the altitude-azimuth pedestal. The secant compensation value changes acutely while the elevation goes high. The pedestal can't follow the target smoothly so as to lose the target near the zenith. The zenith exclusion region, as is the main shortage of the altitude-azimuth pedestal, was analyzed. The conclusion is that the scope of the zenith exclusion region was restricted by three parameters; maximum azimuth angular velocity of tracking mount, flight level and airspeed of the target. And then, the factors that influence high-elevation tracking performance are analyzed. The dynamic delay is usually regarded as the main influencing factor. The effect of equivalent insensitive-zone and random tracking error are often neglected. Nevertheless, it is clearly important to be aware of them in some case. The factors discussed above were tested with the experiment. The actual track data draw a conclusion that the last two factors become the main influencing factors in the case of tracking slow-moving targets. It verified that the theoretical analysis is correct and is very valuable for engineering.