A method used for an induction type power supply system, for detecting whether an intruding metal exists in a power transmission range of the induction type power supply system, includes interrupting at least one driving signal of the induction type power supply system to stop driving a supplying-end coil of the induction type power supply system; obtaining a first attenuation slope during a first period when driving of the supplying-end coil is stopped, and obtaining a second attenuation slope during a second period when driving of the supplying-end coil is stopped; and determining whether the intruding metal exists in the power transmission range of the induction type power supply system according to the first attenuation slope and the second attenuation slope.