To solve the problem of transformer differential protection refusing action, when outside fault CT saturation transfering the same phase inside fault with CT saturation, this paper puts forward a scheme based on differential current sampling points differentia saturated open. For a single power supplying when differential current sampling points of CT saturation periods will be small or presenting interruptive angles; if multiple power supplying and single CT saturation, differential currents return to normal waveforms. It uses ratio braking relations of differential current sampling point and characteristics of the braking current interruptive angle, by identifying total sampling points of meeting ratio braking characteristics and interruptive points within a cyclic wave, to judge whether the fault in the area. The simulation results show that this method is suitable for the identification of the same phase fault about transformer differential protection.