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 were 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.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.