Modern aircraft with high-capacity air variable frequency AC system ask for a well-considered design of the main feeder, and on the basis of the research on the skin effect and proximity effect of its impedance can the optimization possible. The comparative study of impedance of typical main feeder configuration at different frequency level is given, in which the influence of conductor material and gauge, conductor spacing, ground plane elevation and phase sequence are discussed. A series of suggestions for the design are obtained, thereby ensuring the high quality of power supply.