Based on analyzing the structure feature and operation state of silt arrester,the result shows the rational model to determine the seepage line of silt arrester should be to superpose the seepage flow model with horizontal upstream pressure slope upon the seepage flow model with vertical pressure slope of uniform earth damon the permeable stratum base.The solving process can be superposed by means of two type formulas set by the scientists of the former Soviet Union. The practical calculation indicates that the presented method is reliable and reaso nable.