The flow mechanism of gas in organic-rich shale has not been investigated well because of the extreme tightness and complicated structure of the shale reservoir. Due to the multiple spatial scales, the physical properties and upscaling of gas transport in shales have significant uncertainties. A novel, modified 2D ternary-porosity model was proposed to study multiscale gas transport in shales. The model accounts for kerogen, inorganic matter, and granular minerals using physics-based parameters that can be measured independently. Each component part has their own permeability, porosity, and conductivity. In the kerogen part, gas transport is controlled by surface diffusion and adsorption/desorption. In the inorganic matter part, the viscous flow of gas is driven by a pressure gradient. In the granular minerals part, which consists of quartz, pyrite, and ankerite, etc, the porosity of this part is negligible. Therefore, we treated granular minerals as impermeable. Besides, the Klinkenberg effect, tortuosity, shale gas component, and gas flow direction are also applied for. The certain ternary-porosity model was applied to perform history matching of the pulse decay permeameter (PDP) experiment in our laboratory. The results demonstrate that the overall permeability of the core sample under different confining pressures within relatively high effective stress was well-captured by the model. The early- or later-time also play essential roles in the permeability measurement and cannot be ignored simply