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Using the instrumental and visual visibility data from May 2009 to November 2009 from Anshan， Shenyang， Benxi， and Fushun， which are all situated in the urban area of the central Liaoning Province， a detailed statistic analysis is made of the differences between two visibility measurements， in accordance with weather elements and weather phenomena. The results indicate that under the weather condition that there was obstruction to vision， the differences between instrumental and visual visibilities were relatively lower； the more the total cloud cover， the smaller the difference between two observations； the concentration of PM10 was negatively correlated with visibility， and its effect on the visual visibility was greater than that on the instrumental visibility； when the visual visibility was within the range of 1 km to 10 km， the difference between the instrumental and visual visibility measurements was the least； the average absolute errors of both visual instrumental measurements tended to decrease with the decreasing visibility.