Abstract: A method of experimental modal analyses is applied in the prototype tests of dynamic characteristics for the delivery gate of lock of the Three-Gorge Project. The frequency response scope of the field applied force meets the requirement of tests and analyses of hydraulic gates. The structural coupling theory based on the dynamic flexibility is used to identify the modal frequency of 1 rank and 2 rank of the gate-boom coupling system, i.e. 12.5Hz and 32.5Hz respectively, fundamentally out of the high energy zone produced by the hydrodynamic force. Without a special loading, there will be no harmful vibration for the delivery gate. The comparison result of dynamic characteristics between prototype and hydraulic model tests shows that the boundary constraint of the delivery gate in the prototype prevents the occurrence of lateral vibrations and the modal frequency of low ranks corresponding to different vibration shapes is multiplied.