The disclosure relates to a grid-controlled X-ray source, a space X-ray communication system and a space X-ray communication method. The structure of the grid-controlled X-ray source is: one end of the filament is grounded and the other end is connected with the anode of a power supply, the thermionic cathode is located at the side of the filament and the emergence hole thereof faces the filament, the modulation grid is an electrode plate with a small hole which faces the emergence hole of the thermionic cathode, the electronic beam focusing electrode is located on the two sides of the small hole of the modulation grid to form a focusing channel facing the small hole, an electronic beam is focused by the electronic beam focusing electrode and then transmitted to the metallic target anode, wherein the transmitting surface of the metallic target anode faces the outlet of the focusing channel and the other surface is connected with the anode of the power supply, and the output window is located on an reflection path of the electronic beam which is from the metallic target anode. The disclosure solves the technical problems that the signal-to-noise ratio of communication is low, the error rate error rate of communication is high and the speed of communication is low when an X ray is used for implementing communication in the conventional art, and has the advantages of long communication distance and the low error rate of communication.