This paper proposes an initial beacon acquisition method for Free Space Optical（FSO） communications ATP systems on the basis of GPS coordinate calculation and cellular spiral scanning algorithm.It first calculates the azimuth angle and pitch angle of the optical antenna on the basis of the GPS coordinates of both terminals and the antenna rotates accordingly and points to the beacon light approximately so as to minimize the uncertain acquisition regions.Then it scans the regions and leads the beacon light into the coarse tracking Charge-coupled Device（CCD） field of view

realizing the initial acquisition.Ground beacon acquiring experiments verify the effectiveness of this method.