A series of fluid flow tests on different concentrations and different types of salt solutions were conducted on the shale samples through the pressure transfer experiment device to study the influence mechanism of salt ions with different water activities on shale seepage. The experimental results show that the salt solution with the strongest ability to block the pore pressure transmission of Xiushan Shale in Longmaxi Formation is HCOONa among the same concentration of different brines. In addition， the five types and concentrations of salt solutions with better resistance to pore pressure transmission are 20% HCOONa， 5% HCOONa， 20% KCl， 20% HCOOK and 5% NaCl. The highest concentration does not always have the best ability to block shale pore fluid transfer for the same type of salt solution. When the mineral composition is almost the same， the time to penetrate the pores and average permeability of the Xiushan shale of the Longmaxi Formation is 90.11% higher and 99.14% lower than that of the artificially compressed shale. The seepage law of artificially suppressed shale with salt solution is consistent with the real shale. However， the difference between the characterization coefficient is more than 90% for the actual permeability and seepage time. Moreover， a unit distance seepage time model based on water activity and water activity-permeability formulas under different salt ions are proposed for the Xiushan shale of Longmaxi Formation. The research results can provide experimental and theoretical basis for maintaining shale wellbore stability of the Longmaxi Formation with brine drilling fluid.