The threedimensional leakage flow field of lowhysteresis brush seals with a flow deflector were numerically simulated with different axial length of pressure relief chamber at differential pressures drop using a porous medium model calibrated by experimental data.The hysteresis effect of the leakage coefficient was numerically analyzed with the three pressure relief chamber structures in the rising and falling process of pressure drop.The results show that the porous medium model calibrated by experimental data can better predict the leakage flow of the lowhysteresis brush seals.The pressure distribution of the lowhysteresis brush seals with different axial length of pressure relief chamber is nearly the same,and there is almost no pressure gradient between the brush pack and the backing plate because of the existence of pressure relief chamber.The leakage coefficient is increased rapidly with the increase of the pressure drop and then tends to be stable.When the axial length of pressure relief chamber is 0.5 mm,the leakage coefficient is the smallest,while the hysteres is effect is more significant.The research result can contribute to the study of leakage and hysteresis effect and structural design for lowhysteresis brush seals.