The fuel pressure regulator, usually mounted on the fuel rail, is used to maintain a constant pressure drive from the fuel rail to the intake manifold. After 15,000-45,000 miles of operation the regulator sometimes is unable to function properly due to the retainer failure. This work is to identify the possible causes and to compare the performance of regulators with different retainers through CFD (computational fluid dynamic) and FE (finite element) structural analysis.In CFD analysis, we want to find out if any undesired fuel vapor exists in the fuel pressure regulator. Unlike liquid fuel, the fuel vapor does not provide any cushion between the valve and the valve seat to ease up the impact force. The existence of fuel vapor may cause more wear-out at valve seat. Since the valve opening in CFD domain is a function of pressure difference between the fuel rail and the intake manifold, one set of dynamic equations is solved to determine the valve openings at various operating conditions. This set of equations was also applied to simulate the valve vibration in the air buzz test. The calculated vibration frequency is close to the measured value.Mechanisms related to retainer failure, i.e., wear-out and resonant excitement, are analyzed for two different retainers. FE structural analysis was employed to study the retainer's natural frequency and stress distribution under the pull-out test conditions. Since wear-out is related to stress level on the contact surface, the new design with lower stress is concluded to have a longer life cycles. Failure of the old design can be also a result of resonant excitement. These predictions are consistent with the experimental observation.