As a result of the transfer function analysis on the casual relationship between Andong Dam water level and fog time in Andong City from March of 1981 to December of 1992, it should be referring to monthly increases in the water level having an effect on 0.89 hour per m increases in the fog time with 4 months delay. It is evident, hence, the artificial lake of the dam is one of the direct causes of fog. Based upon this objective evidence, water resources development policy and dam managment policy must be formulated.