Abstract: A permeation test system of constant water head composed of Mariotte flash and permeation instrument was designed to study effect of geotextile placement position and layer number on soil permeability, and upper load influence on permeability coefficient of geotextiles．Geotextile was found to reduce effectively permeability coefficient of soil but increase height of critical seepage failure water head, thus improving permeability stability of soil．However, increase in upper load of geotextile was found to increase permeability coefficient of geotextile itself．Permeability coefficient was found to decrease with enhanced position of geotextile and increased layer numbers．Seepage failure critical water head height increased with increasing geotextile layers．For monolayer geotextile, when geotextile was placed in middle position of soil, seepage failure critical water head height reached a maximum, seepage stability of soil was the best．With the formula derived in this work, a relationship between permeability coefficient of soil and buried depth of geotextile in soil can be calculated．