In the near space communication system, the atmosphere, rain, flash will cause the open space link channel quality deterioration. In this paper, near space airship is taken as a communications platform, the Ka-band near space communication channel propagation characteristics of radio waves are analyzed, the focal point is put on analyzing the impact of rainfall on the signal fading. Based on this, the channel model and simulation model of Ka-band near space communication channel are established, and the simulation of the BER performance in Matlab environment is conducted, which provide a theoretical basis for the analysis of close spatial link and the resistance to Rain Fade.