Abstract: The Computational Fluid Dynamics（CFD） method is employed to numerically simulate the working process and the hydrodynamic characteristics of a safety valve.When the inlet pressure is larger than the cracking pressure,the safety valve begins to vend gas for decompression through the moving of valve clack,and the flow zone in the safety is changed.In order to make the computed model adaptive,relevant dynamic meshes which are created or suspended according to the move of valve clack are adopted to update the CFD model in every time step.As an example,the performance of the safety valve with spring direct in compression is studied,and the relation of different static inlet pressures to the spool stroke、flux and the axial force acting on the valve clack are attained.In addition,data about flow field in safety valve is obtained through the unsteady CFD simulation,which indicates that CFD can be a strong tool for us to study the hydrodynamic characteristics of safety valve.