A power source used in wireless power transfer generates an AC wave to transfer electric power to a load which is not connected electrically but connected electromagnetically to the power source. In this paper, the power and efficiency are compared when a sinusoidal and a square waves which are typical AC waves are applied as power source voltage outputs. The condition under which the two waves respectively transfer equivalent power with electric wires is examined to figure out the effect of different waves. Then the power and efficiency are calculated by a mathematical approach with practical values of elements on various situations. Finally, this paper explores how input waves should be chosen for ideal wireless power transfer.