Abstract: The influence of seepage direction on the silt permeability are studied. The vertical and horizontal seepage tests of silty sand are carried out by using the self-designed devices. The critical gradient and deformation characteristics of silt under two different seepage directions are obtained in the tests. When the other influencing factors such as gradation, density and pore size are the same, the vertical hydraulic gradient of horizontal seepage of silt is generally 44% higher than the critical one, and the horizontal seepage is generally higher than the vertical one. The data can be used for design of seepage control of the silt. Based on the indoor model tests, the micro-mechanical model is used to analyze and simulate the seepage behavior of the silt under vertical and horizontal directions. The hydraulic gradients of the two seepage directions calculated by numerical model are consistent with the test ones. The loss of particle clusters occurs in horizontal and vertical seepages at hydraulic gradients of 0.8 and 0.4, respectively. The research results may provide a theoretical basis for the design of seepage control in water conservancy and hydropower projects with silt layer.