A numerical simulation model for the internal meshing cycloidal rotor expander was developed using computational fluid dynamics software to perform numerical calculations. The study explores how factors like rotational speed, inlet pressure, and inlet temperature affect the mass flow rate of air within the expander. To evaluate the accuracy and validity of the simulation, an experimental system was also built, and corresponding experimental research was conducted. Both simulation and experimental results indicated that, at a fixed inlet pressure, the air mass flow rate in the expander increases with rising rotational speed. At a constant rotational speed, the inlet flow rate rises as pressure increases. Conversely, with constant inlet pressure and rotational speed, the inlet flow rate decreases as inlet temperature rises. The simulation results for inlet flow rate were compared with experimental data, showing good agreement, with a maximum deviation of around 5% at 293.15 K and about 7% when the pressure is held at 0.20 MPa. These findings confirm the reasonableness and reliability of the numerical calculations, offering valuable insights for optimizing the expander’s structure.