This paper proposes a simple but accurate method for calculating the dynamic properties of an air spring employing an orifice to produce a damping force. Air springs are very common in rail, automobile, and vibration isolation applications. However, because this type of air spring has non-linear flow characteristics, an accurate analysis approach is yet to be proposed up to the present day. The restoring and damping force in an air spring with an orifice damper vary with the amplitude of the body. This amplitude dependency has not been considered in previous studies. Proposed herein is a simple model for calculating the air spring constant and damping coefficient. However, iterative calculation is required due to the non-linearity of the spring. The theoretical and experimental results are found to agree well each other. The theoretical equations provide an effective tool for air spring design.