The expansion chamber mufflers compounding with the perforated panels are commonly used in the suppression of intermittent exhaust noise (IEN) generated by the exhaust air from the cylinder and ducts of pneumatic devices. The flow resistance and noise reduction performances of IEN are both important. A simplified aerodynamic model is presented to study the flow characteristics in the pneumatic cylinder and chambers of the muffler with perforated panels. The relationship between pressure and mass flow rate is established in the transient exhaust process. Validation experiments measuring the cylinder pressure and exhaust noise of the pneumatic friction clutch and brake (PFC/B) exhaust system installed a three-level perforated panel muffler which can be separated show that the calculated results are very close to that of the actual exhaust process.