Abstract：The fault zones consist of main discontinuities with low dip angle in the dam foundation rockmasses of Xiluodu hydroelectric station. Therefore，investigating the characteristic of seepage in fault zones can instruct the design of impervious curtain in the dam foundation. The in-situ seepage tests in fault zones and their results are introduced. The factors affecting the permeability，critical gradient，failure gradient and the procedure of seepage are analyzed.
