With the help of system reliability analysis method, the distribution of Weibull, Gamma and Log-normal that can be used to describe the system service behavior characteristics was selected to establish models of probability distributions according to the sequences of typical dam sections which has great significance to achieve the dam safety monitoring.The distribution that can describe the dam service behavior characteristics most objectively was chosen based on the criterion of the theory of the maximum entropy. The work that comparison between probability distributions and estimation of the value of displacement early warning was finished combined with the dam accident probability. The results showed that: the best model that can describe the typical dam sections service behavior characteristics most objectively is three-parameter Weibull distribution, it can be a more reliable way to estimate the value of dam displacement early warning.