During running process, the effect of dynamic loads is quite complex. So determining dynamic characteristics of supporting structure are of great importance when making hydro plant's dynamic analysis. However, conventional testing measures often cause intensive destruction or are too complicated to implement. In order to solving above problems，this paper，basing on principle of dynamics, applies the test data to analyze the structure vibration and variability of loads during machine halting process，and further puts forward a new method to identify dynamic characteristics of hydro plants supporting structure using machine halting process. The test data comes from prototype observation in Lijiaxia's power house structure of two-row placed units. The method, combining unit test and structure test result, and fully using advantage of wavelet analysis, successfully overcomes poor factor like long variation time of loads，vibration fluctuation，etc.,when analyzing halting problem.