A global quantum satellite communication scheme that transmits information by single photon through free space is proposed. To reduce the influence of atmosphere, this system mainly adopts ground to satellite communication and satellite to satellite communication, assisted with the ground to ground communication. Analysis is made to the impact of the atmospheric channel, the background noise and the Faraday effect of geomagnetic field on the choice of wavelength, and the feasibility of the communication scheme is studied. Simulation analysis is made to this scheme's link attenuation requirements. The result shows that the communication scheme can satisfy the requirement of the communication link.