The Sichuan Basin is an important natural gas production base in China, where carbonate gas reservoirs have been developed on a considerable scale. This type of gas reservoir are characterized by a developed fracture–vug system, ultra low porosity and low permeability. Depleted gas reservoirs can be rebuilt into underground gas storage (hereinafter referred to as UGS) to meet the demands of natural gas supply during peak natural gas consumption in winter. Unfortunately, however, there is no mature experience at home that can be used for the construction of fractured–vuggy carbonate gas-reservoir UGSs. In addition, the flow behaviors in fractured–vuggy UGSs during high-rate injection and production are an important basis for verifying the feasibility of UGS construction and operation. Taking the first fractured–vuggy UGS (Moujiaping UGS) built by PetroChina Southwest Oil & Gasfield Company as an example, this paper designs a fracture–vug combination scheme with reservoir characteristics based on the seismic and outcrop data, and establishes a 3D digital core model. Then, numerical simulation is carried out by using the model, and the variation laws of gas pressure and flow rate in different areas in the process of high-rate production are calculated. Finally, the flow behaviors and storage utilization mechanisms of fractured–vuggy UGSs are analyzed on a microscopic scale. And the following research results are obtained. First, the higher the reservoir permeability, the faster the gas utilization in fractures and vugs, and the more significant the flow hysteresis effect. Second, under the condition of the same fracture–vug combination, the gas flow rate and production rate are proportional to the production pressure gradient. The production pressure gradient has a significant impact on gas flow behaviors. Third, narrow fractures present in the fracture-vuggy system, and smaller fracture aperture has a more significant impact on the flow hysteresis effect. Fourth, the more complicated the fracture–vug combination and the morphological structure, the more significant the flow hysteresis. In conclusion, this mothed can provide an important theoretical basis for researching the flow behaviors and storage utilization mechanisms of fractured–vuggy carbonate UGSs in the process of injection and production, as well as a technical support for the construction of similar UGSs. © 2023 Natural Gas Industry Journal Agency. All rights reserved.