The paper used river hydrodynamic model to simulate the process of water level variation.Through the analysis of reliability to calculate hydrological failure probability,it combined with reserve drown value to evaluate embankment hydrologic crash risk. As an example for empirical calculation in Suzhou,it got hydrological accident probability and expected loss value under the existing scheduling scheme. The results showed that embankment hydrologic accident probability is so large that it shows the emergency demand for the increase of embankment height. The paper setup the base of relationship between benefit, cost and height of embankment and got the optimal height of embankment heightening in order to provide the basis for the decision-making of emergency preparation during flood season.