The biggest challenge for free space optical(FSO) communication systems is the attenuation/fluctuation of light intensity caused by influence of atmospheric turbulence in long distance communication, resulting in communication link interruption. A method to calculate the link loss due to atmospheric turbulence, based on lognormal statistics of the received power, was presented. It can be used to evaluate the system parameters in FSO communication system. The effects of different intensity turbulence were simulated, and the relationship between optical communication link loss and transmission distance at 850 nm and 1 550 nm wavelengths at receiving terminals of 2 cm and 20 cm was obtained. Then the simulated analysis results were used to design a FSO communication system with a receiving aperture of 20 cm, which could transmit HD image and video at a distance of about 2 km under strong turbulence conditions. The transmission rate of the FSO communication system was 1 Gpbs which could meet the sharpness and real-time performance of large amount of uncompressed data transmission compared with the 4 G networks.