Digital simulation technique is introduced in this paper to analyze the dynamic response of a two-stage relief valve. The results indicate that the dynamic properties of the valve is quite satisfactory and therefore it could be readily adapted to suit the computer aided thermodynamic test (CATT) system so far as the system fluid capacibance is big enough. It is also presented in this paper that the FORTRAN programme built up is very effective and could easily be expanded to use in other hydraulic components.