Abstract: At present the dams built in our country are more and more numerous higher and larger. As time goes on, the dams are often subjected to action of low temperature and high water level. And age-harden year by year, therefore large dam safety monitoring have become a important research subject that is paid attention to our country even in the world. This article discoursed deterministic model and statistical model which established on the basis of displacement actual measurement data on the 13# buttress of Fu Ziling dam in the fourth period (from June of 1983to Dec. of 1984), and which is used for forecasting horizontal displacement of dam top (form Jan. of 1985 to June of 1986). And for comparing the forecast actual effect, the forecast precision and surveillance action to dam safety operation.?