On 9 August 2019, a major power blackout occurred in the great Britain power grid, causing power outage in some cities including London, and affected about 1 million people. It is necessary to find the reason to provide reference for the gird operation of China. The accident is summarized and the oscillation in the wind farm is discussed in detail. The reflection and analysis about the oscillation is presented considering the serial oscillation event, including typical characteristic and remaining problems. The new characteristic of oscillation about power grid which connected a large scale renewable plants is described, the shortcoming of wide area measurement system(WAMS) is demonstrated, and a new method of real-time monitoring of oscillation based on wide-frequency measurement is presented. The scheme about implement provides new method for operation and supervisory of power electronics dominated power system and improves the security and stability of future grid.