According to the horizontal visibility data observed by manual and automatic ways of Anqing meteorological station in 2012, differences between them were analyzed from two aspects: different observation time and different weather phenomena. Correlation of visibility between manual and automatic observations was calculated using correlation coefficient method. Differences between them were also analyzed with its statistical characteristics and hypotheses tested by the way of sign test and Wilcoxon rank sum test. The results showed that a positive association can be obtained between visibility detected by manual observation and automatic one in different times, and a significant correlation is also found under different weather. The difference of visibility between them is notable when times and weather are different.