A novel bellows-type flow regulator was designed with the ability to maintain a steady thrust level and to adjust the thrust of a liquid rocket engine. The flow regulator showed good performance not only in maintaining the flow rate despite changes in the pressure difference across the flow regulator, but also in adjusting the flow rate in response to a changing shaft angle. A mathematical static model of the flow regulator was developed. A design criterion for ideal performance of the flow regulator was derived by theoretical analysis of the mathematical model. It was established that the main design parameters of the flow regulator affecting flow rate maintenance were the number and the width of ports in the 2nd throttle. The static characteristics predicted by the mathematical model show good agreement with experimental results, thus validating the mathematical model.