Compared with conventional sandstone gas reservoirs, carbonate gas reservoirs have multiple media such as pores and fractures, poor reservoir matrix and complex seepage mechanism. In this paper, a multi-media model conforming to carbonate gas reservoirs is constructed through the fine characterization and numerical simulation of pores and fractures of carbonate gas reservoirs, and the complex seepage mechanism of carbonate gas reservoirs is explored. Conclusions: (1) A new method for constructing complex multi model reservoir models has been proposed, which combines core CT scanning and builds pore models based on digital cores. Furthermore, by statistically analyzing the distribution patterns of karst caves and fractures in core samples, and combining Monte Carlo method, a multi medium pore fracture cavity model that conforms to the complex seepage mechanism of carbonate rocks has been constructed; (2) Permeability calculation under different combinations of pores, fractures, and holes have been achieved, and the accuracy of permeability calculation by taking the average value through multiple permeability calculations have been improved. This study provides a new research method for accurately calculating the permeability of complex and strongly heterogeneous gas reservoirs, which can further support the evaluation of the mobility of low-grade reserves.