In order to solve the problem that traditional thermal power unit over-speed protection control characteristics can not adapt to different forms of fault on the grid or the unit, and to improve the control strategy, strengthen the power grid stability, enhance security unit, this paper presents an improved over-speed protection of thermal power unit based on the control of automatic safety device. By collecting information, processing and distributing the commands through the regional stability control system, this new protection realizes the combination of automatic safety device and over-speed protection, which can achieve the purpose to prevent the simultaneous act of over-speed protection units within the same region. Analysis indicates that the new protection with strong operability not only ensures the original unit safety barrier from being weakened but also improves power system stability, which provide a new way to solve the problem of a high-frequency isolated network system.