The free-space quantum key distribution (QKD) technology has become one of the research hotspots in the field of quantum communications, and the continuous variable QKD and the discrete variable QKD are two major technical branches of this technology. The recent research progresses of free space QKD technology at home and abroad are reviewed. From the viewpoint of practical applications, the technical difficulties of these two branches are compared and analyzed. The phenomena like the background light interference, the single photon depolarization characteristics in the atmospheric channel and the phase distortion caused by turbulence are analyzed emphatically, and the development foreground of free space QKD technology is prospected.