In the Ka-band satellite communications, signal fading caused by rain reduces service quality of satellite links, and open-loop uplink power control is one of the most cost-effective rain fade countermeasure technique. In this paper, an identification method to the real time clear-sky reference level is presented，it alleviates affects of rapid variations in rain intensity. The specific realized circuits of fade estimation are studied in detail, and the fade estimation is a key part in open-loop uplink power control algorithm .