In order to detect the fundamental positive and negative sequence currents and harmonic currents effectively and efficiently in electrified railway power systems， a new detecting method based on Fryze-Buchholz-Dpenbrock（FBD） method is proposed. In order to construct the fundamental positive and negative sequence reference voltages， phase locking loop（PLL） is used to track a phase of asymmetrical three-phase or distortion voltage to obtain frequency and phase information. Using constructed positive and negative sequence reference voltages and detected three-phase currents， it can obtain the corresponding positive and negative sequence equivalent conductances. After filtering the conductances with low-pass filter（LPF）， positive and negative sequence DC components can be obtained. Fundamental positive and negative sequence currents can then be calculated by multiplying the positive and negative DC components with the corresponding positive and negative sequence reference voltages. Harmonic currents can be obtained by subtracting the fundamental positive and negative sequence currents from the total currents. Because this method only requires detecting one fundamental frequency and phase of system three-phase voltages， it can be used under asymmetrical or distorted system voltages. This method does not require Park and dq transformations and the computational cost is very low. The simulation results confirm the accuracy and validity of the method.