The storage space of fracture-cavity carbonate reservoirs is primarily composed of fractures, cavities, and matrix pores. Among them, fractures and cavities exhibit highly random distribution, serving as the main storage spaces and seepage pathways for oil and gas. The strong heterogeneity of these reservoirs leads to highly complex fluid flow behavior, characterized by the coexistence of free flow occurring in cavities and seepage flow in fractures. Indoor physical simulation experiments are usually required to reveal the fluid distribution patterns and unique flow phenomena within the reservoir. However, current physical models for fracture-cavity systems struggle to meet both high-pressure resistance and visualization requirements, thus limiting the investigation of fluid flow mechanisms under reservoir conditions. To accurately characterize fluid flow in fracture-cavity reservoirs while reducing experimental research costs, the feasibility of fluid flow experiment simulations in fracture-cavity reservoirs was explored based on fluid dynamics and computer simulation technology. By simulating and analyzing the flow characteristics in the free flow and seepage regions of the fractured-vuggy physical model, it was found that under reservoir temperature and pressure conditions, fluid flow in the physical model primarily followed low Reynolds number Stokes flow. Based on this, the traditional free flow equation was simplified, and a unified momentum equation was established to describe both free flow and seepage in the model. Parameters such as the viscous resistance coefficient were introduced into the Euler equations to characterize multiphase flow characteristics in the seepage region, achieving an integrated simulation of different flow regimes in the fracture-cavity model. A 3D fracture-cavity digital model was selected for flow simulation, and the comparison of simulation results verified the reliability of the unified flow model. The simulation results indicated that for typical fracture-cavity physical model flow experiments, the laminar flow model based on Stokes equation could achieve the simulation accuracy of the traditional Darcy-Navier-Stokes (Darcy-NS) coupled model, with strong reliability, while significantly improving computational efficiency. This provides a new research method for the study of flow mechanisms in fracture-cavity reservoirs.