Abstract: Gradient ratio tests are carried out to study the influence of uniaxial tensile strain on the filtration characteristics of geotextiles. Four kinds of geotextiles (two needle-punched nonwoven and two slit-film woven) are employed in the tests. The filtration systems are composed of the geotextiles under designed uniaxial strains and gap-graded soils. The variations of the mean flow rate, the weight of soil passing through the geotextile and the gradient ratio with strains are analyzed based on the filtration criteria. The experimental results illustrate that the permeability and anti-clogging capabilities of woven geotextiles increase with the increase of the uniaxial tensile strain, but the retention capabilities decrease. The influence of tensile strain on nonwoven geotextiles is just the reverse. Moreover, the thicker the geotextiles are, the larger the influence of strain is.