Based on the synoptic routine analysis, a regression estimation of event probabilities to forecast scatter of radiation fog at Xianyang Airport is developed. An analysis is made by selecting 95 events of radiation fog at 6:00 a.m. during the period from 1992 to 2002 and thinking over the probabilities of scatter of the radiation fog in 4 hours. The regression equation is significant on the statistic F-test, and the accuracy of returning-forecast and testing-forecast are over 78%.