The hysteresis effect of seepage variation caused by reservoir water level variation is deeply studied; and then a hysteresis seepage model is presented. By use of this model and optimization analysis,hysteresis days and effective water depth upstream are determined. By introducing effective water depth upstream
an instability seepage problem is converted to a stability seepage one. Based on this simplification and combining measured data and seepage analysis
an analytic model for base flow of dam seepage is proposed. The example shows that the model can simulate behavior of base flow.