The frequency characteristics of islanding operation are introduced firstly. The magnitude of balance between electromagnetic power and the original motive power and the inertia of the system are the critical factors that affect the frequency. Based on the possible over-frequency problems during the isolated operation of the regional network, the configuration principles of over frequency generator tripping are proposed. Taking an actual grid as an example, an adaptable and efficient configuration solution of over frequency generator tripping is made according to the principles. In addition, the coordination between over frequency generator tripping and over-speed protection controller is studied. This paper brings forward meaningful reference configuration principles for over frequency generator tripping that is suitable to small-capacity regional power grid which is in infirm interconnections.