Clogging criterion is an important part of filter criterion. Gradient ratio test is used to judge the clogging performances of geotex tile, but the practical situation of geotextile is oversimplified in this test and the test result(gradient ratio) is not sensitive to the changes of soil and geotextile under water flow. In order to make gradient ratio test perform more efficient, the gradient ratio formulas were modified and the effects of exterior factors on seepage, such as tensile stress of geotextile, compression stress of filtration system, cyclic flow, dynamic load, and granular drainage layer, were considered in the tests, and then the mechanism of anti - clogging of geotextile under these factors was researched.