The invention provides a spatial optical communication method and a spatial optical communication system. The method comprises the following steps: a low-orbit satellite onboard communication device periodically updates satellite ephemeris information by using a onboard navigation receiver and reports the satellite ephemeris information to a top data transmission satellite; a relay satellite packages all integrated low-orbit satellite ephemeris information into frames, and periodically broadcasts the frames; a low-orbit satellite receives the broadcast information, and calculates the spatial position coordinates of other satellites at different times according to the broadcast information; an onboard antenna tracking and pointing system (ATP system) performs data analysis according to the spatial position coordinates and then quickly adjusts a beam to perform tracking and pointing and adjusts the transmit power. The present invention provides a fast, efficient and reliable inter-satellite networking mechanism.