A sectional vane for vertical axis wind power generator includes a frame unit and a plurality of vane units. The frame unit is fixedly mounted to a main shaft of the wind power generator, and includes an upper frame member and at least one lower frame member. The upper and lower frame members are provided on inner side with an upper and a lower guide rail, respectively. The vane unit includes a vane body having an upper and a lower guide channel provided on a top and a bottom, respectively, corresponding to the upper and the lower guide rail. The vane units are assembled to the frame unit between the upper and the lower frame member through engagement of the guide channels with the guide rails. The sectional vane can be varied in height and area by providing different numbers of lower frame members and vane units.