Compensating current control is the key tache to accomplish the various functions of active power filter. In the text, a single phase active power filter is proposed based on suppressing the electrified railway system harmonic current.One-cycle control of double-direction compensating control scheme have a great impact on the performance of it. And simulative model is established based on one-cycle control of double-direction compensating control schem. The simulative result shows that the current control schem above can be used in the electrified railway system to control harmonic current and filter a majority of the electric locomotive harmonic current and lower THD of the source current.