The accurate and timely visibility data is a crucial factor when the effect of a tmospheric attenuation on the performance of free space optical (FSO) communic ation system is analyzed. Firstly,the shortcoming of the current method with obtaining the visibility data is pointed out,and the inversion data of laser radar (LADAR) is very suitable for estimating the performance of FSO link.Secondly,t he way of inverting the horizontal visibility data from the laser radar observation data is introduced, and then the all-day visibility data is received on January 18because there is special weather in Yantai region. At t he same time,combining the 80% threshold value of relative humidity,the conversion process between fog and haz e is analyzed briefly on that day.Lastly,based on the measured value of the la ser radar,the bit error rate performance of FSO communication (BER) is analyzed in real time under the special weather condition by set t ing some appropriate parameters.The analysis results show that fog is far more likely to cause the BER performance degradation of FSO communication system than haze.The conclusion of this paper will provide very valuable guidan ce for building the practical FSO communication link in this region.