In order to improve gasoline pump’s small amount of refueling cavity, the whole pump system vibrate and produce noise problem, established relief valve three-dimensional model of the internal flow field in accordance with the structure and parameters of the actual relief valve , studied the flow field of the relief valve with the application of computational fluid dynamics software Fluent , use the moving mesh grid technology UDF to research valve’s dynamic characteristic, simulate the process from open until the stability, get the distribution of pressure field, spool movement speed, force and displacement inside of The relief valve change with time. Through analysis get the reason why the pump system vibration and produce noise is that relief valve spool’s back and forth concussions, which lead to flow pulsation at exit and then cause noise and vibration. Therefore to optimize the fit clearance between the spool and valve body, and simulate the dynamic characteristics of the relief valve under five different dimensions of girth type. The result shows that, when the fit clearance dimension of girth type is equal to 0.1mm, relief valve movement more gentle than not and pulsation rate of the flow reduced. This research work for the optimal design of the valve provides a theory basis, for practical work to reduce the noise of the relief valve provides ideas. Through experiment shows when value stays between 0.09 mm and 0.1 mm the noise of the relief valve decline significantly, verify the proposed theory in the text. Through the comparison, simulation and experimental results further confirmed the feasibility of this method, the conclusion and methods for the follow-up research work has certain referential significance.