High-dimensional wireless power transfer (WPT) systems have received increasing attention for charging mobile devices. With the receivers have higher spatial freedom, the systems are more susceptible to the metal objects in the surroundings. However, conventional methods for metal object detection (MOD) can't satisfy the requirements of safety and stability of new systems. This paper proposed a metal detection method which is more suitable for high-dimensional WPT systems. The key feature of the proposed method is combining load impedance and input power characteristics curves to determine whether the receiver is a metal object or a coil. And the influence of the metal is discussed in the circuit and magnetic model. The method is theoretically proven by the simulation calculation. And the experiments verified that the method can accurately detect the metal objects by setting the threshold curves.