The present invention provides a vertical-axis windpower fan unit using a central axle having modulized design for assembling or disassembling quickly and includes supporting arms with capability of weight adjustment so as to balance the rotation of the fan unit. In one embodiment, the present invention further provides a coaxial fan module comprising a plurality of fan units coupled sequentially wherein a blade of each fan unit is disposed in the middle position with respect to the two blades of the adjacent fan unit for reducing unbalance and eliminating vibrational noise while the fan module is rotating. In addition, in another embodiment, the present invention further provides a power generating system comprising the coaxial fan module and a power generator unit coupled to the coaxial fan module so as to generate electricity.