Conception of limit soil-retained state was originated. Four kinds of woven steel-wire nets with different opening sizes were adopted in the filtration tests with silt. Test results show that filtration system approached limit soil-retained state when the ratio of the opening size of net filter (O) to the characteristic particle size (d85) of the silt upped to 12. Filtration system under limit soil-retained state kept stable during 26 hours of cyclic flow. And the filtration system still maintained its stability under the unidirectional submersed flow whose hydraulic gradient was increased from 3.8 to 9.1 gradually and maintained at 9.1 for 453.25 hours. Filtration system lost its stability under the unidirectional free flow whose hydraulic gradient was increased from 5.3 to 12.7 gradually and maintained at 12.7 for 261.83 hours. Researches on limit soil-retained state redound to a more reasonable upper limit of filter opening size and less clogging for filtration design.