A detection method for discovering an unexploded ordnance includes: surrounding a detection region with a transmitting coil and surrounding a detection site with a second receiving coil; conducting the transmitting coil with a second electric current; respectively acquiring a plurality of second feedback signals at a plurality of second feedback time points; partitioning the transmitting coil into a plurality of dipoles, and acquiring a plurality of distance values r respectively between the plurality of dipoles and the detection site; respectively calculating feedback depths according to feedback time periods; respectively calculating apparent resistivity values corresponding to the feedback depths; obtaining an apparent resistivity distribution in depth at the detection site according to the apparent resistivity values and the feedback depths; and judging whether there is any unexploded ordnance at the detection site according to the apparent resistivity distribution in depth.