The excitation characteristics of transformer ferromagnetic material present nonlinearity, which leads to inrush current phenomenon in the process of transformer closing. Overcurrent protection often acts reflecting single current amplitude characteristic. When transformer closing, inrush current and through current in the neighboring region may cause correlative overcurrent protection malfunctions. This paper, from the view of sequence components, constructs a mark function. The mark function can distinguish fault and inrush current by its value and sudden change. The simulation by PSCAD/EMTDC tool shows that this function can reflect the changes of power network structure fully, and the function can distinguish transformer inrush current and fault effectively. The application of mark function to current protections can reduce the effect of inrush current on overcurrent protections.