The theoretical model of blow-down effect of brush seals was analyzed. The three-dimensional transient numerical model of blow-down effect of brush seals based on arbitrary Lagrange-Euler（ALE） fluid-structure interaction method was established. The axial

radial and sectional deflection characteristics of bristles were studied respectively. The radial blow-down displacements of bristles were analyzed quantitatively

and the induced mechanism of blow-down effect of brush seals was revealed. The results showed that the leakage can be calculated more accurately with consideration of blow-down effect

because the bristle radial clearance was reduced by blow-down effect. Blow-down effect of brush seals presented an unsteady deflection with bristle oscillation. Compared with bristle cross section in the radial middle and end position of backing plate

blow-down effect and bristle oscillation of bristle tip were stronger. Bristles had more radial blow-down displacements and stronger bristle oscillation with the increase of inlet-outlet pressure ratio. When the inlet-outlet pressure ratio was 2

3 and 4

the maximum radial blow-down displacement of bristles in the middle of bristle pack was 0.004

0.010 mm and 0.019 mm

respectively

under the studied condition. The initial condition for the bristles with a certain circumferential lay angle and the radial pressure gradient in bristle pack contributed to the induced blow-down effect

and blow-down effect was further influenced by the normal pressure and the tangential friction between bristles. Blow-down effect of brush seals can be weakened by increasing the circumferential lay angle.