Abstract: This paper presents the statistic analysis of duration curves, which have been frequently used in channel engineering, water power engineering, and water supply and sewerage work. It is supposed that the duration curve is a stationary stochastic process, and, therefore, the self-regression model is chosen for the curve. The paper shows that with this model the computational results fit the survey data very well,and the duration curve is determinnate. As the mathematical model is very simple, the high accuracy duration water levels of different design standard can be produced through simple calculations.