There are many methods to improve the qualities of free optical communication (FSO) .It is one of the effective ways to
improve anti-interference and noise faculty. Disadvantage factors and receiver background light in the laser
communication result in interference. Noise is mostly in the receiver. The paper introduces in the FSO system, the laser
signal which transmits in the atmosphere random channel is effected by atmosphere absorption, scattering, atmospheric
turbulence and interference by the building sloshing; when received, it is effected by the ground light interference.
Accordingly, we compare some proposed method with others. Based on the sources of noise, we detail the receiver noise
and give some advices on designing photoelectric detective circuit. This study on FSO has a theoretical reference value.
Based on the transmission character of atmospheric channel and the model of single-scattering and multiple-scattering,
the influence of laser pulse intensity and pulse broadening in different atmosphere are studied in this paper. According
to the simulation results, it can be concluded that the laser pulse intensity passing though atmospheric channel is
inversely proportional to scattering coefficient and transmitting distance, contrarily the pulse width directly proportional
to the mean square scattering angle of particle and the single scattering ratio. The research results have the important
value for achieving the engineering application of free-space optical communication.