A special curved magnetic filter was developed to investigate the effect of different bias mode on the transport of cathode arc plasma through the curved magnetic filter. The relation between the ion output of the filter and the cathode arc current was determined. Each part of the wall inside the duct interacted with the plasma independently. Two kinds of ion flux onto the duct wall were presented and they played different roles when cathode arc current changed. It was found that whole duct bias was more effective in plasma transport through the filter than the Bilek plate bias

although the Bilek plate (or the outer-wall inside the duct) contributed most part of ion output of curved magnetic filter when they were positively biased.