Change Trend of Atmosphere Visibility from 1951 to 2006 in Guilin

The paper uses cumulate percent method, ridit value method and ¿very good day¿ method, to analyzes data of atmosphere visibility in Guilin city from 1951 to 2006 year. The result shows that atmosphere visibility ascends in 1950s, reduces since 1960 year, and reduce speed is slower from 1981 to 2006 year than that from 1960 to 1979 year. The paper also concludes that as the observe criterion of atmosphere visibility is amended in 1980 year, the low value of atmosphere visibility and middle value of atmosphere visibility, do not change much spanning 1980 year, while the high value of atmosphere visibility changes much spanning 1980 year, so as ridit value and ¿very good day¿ which has obvious correlativeness with the high value of atmosphere.