Abstract: In the discharge piping system of a storage tank, the quiker the valve closing, the higher the surge pressure and the smaller the delay flow will be. Therefore, it is of great importance to optimize valve closing mode for purpose of achieving low surge pressure and minimum delay flow. The coventional optimization design method, sufferring from such drawbacks as stereotyped objective functions, big errors, low operability. etc. can not achieve the goal satisfactorily. This problem has heen solved successfully by means of the optimization design of simulation analysis. This method's correct and achievable design result can be contributed to: ① characteristic equation used for surge parameter calculation. ② surge simulation analysis made for e'sch possible valve closing mode, and ③ full considerations taken for every kind of constraint to the valve. On the basts of the principle of optimization design. shown in the paper is the comparation block diagram for the optimal valve closing mode, which is leelpful for realizing calculation in computer system. The influence of pipe filling on optimal valve closing mode is revealed through studying cases and analyzing the results of optumization design.