Abstract: Rain attenuation is the dominant propagation impairment for information systems operating at frequencies above about 10GHz. Reasonable strategies must be adopted to compensate the attenuation caused by rainfall. In order to provide technical support for adaptive power control of earth-space links, the gray system theory was first used to carry out the　rain attenuation short-term prediction. The selection principle of grey system model and parameters is proposed herein by analysis. Lastly, the observation of Ka-band earth-space link in Haikou, China has been selected to verify the new model,and the rain attenuation has been forecasted with the interval of 1 s and 5 s based upon the real-time rain attenuation data.The results show that the rain attenuation predictions using the grey system theory coincide well with the measured data.