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The main influencing parameters for water-hammer prevention characteristic of air valves are analyzed through experiment. The result indicates that the air valve with reasonable size and installation position can prevent high water hammer pressure caused by water column separation. However, the prevention effect is impressible to the size and installation position of air valve: too large size will cause large pressure during the venting process, while too little size can not obtain prevention effect for insufficient air quantity and slow intake speed. So the air valve should have rapid intake speed and slow venting speed. For the experimental system in this study, the air valve should be installed in the position where the water column separation occurs firstly. Based on the analysis result, the optimization model for the air valve parameters and closure procedure of pump outlet valve is set up and solved by using genetic arithmetic. In the end, the above optimization method is used for the water-hammer prevention of a practical water-supply project and the suggestion of suitable prevention measure is proposed. 