Near magnetic field variation detection system and detection method thereof

A detection method for near magnetic field variation comprising following steps of: measuring magnetic field by a first magnetic sensor and a second magnetic sensor, wherein the first magnetic sensor and the second magnetic sensor are configured in a field or a surrounding area around the field; and calculating a magnetic field difference, wherein the magnetic field difference is (1) the magnitude of the difference of a first magnetic field vector measured by the first magnetic sensor and a second magnetic field vector measured by the second magnetic sensor, or (2) the magnitude of the difference of a first magnetic field vector component along a feature direction measured by the first magnetic sensor and a second magnetic field vector component along the feature direction measured by the second magnetic sensor, wherein (a) when the magnetic field difference continues to be greater than a feature threshold value for a feature period of time, or (b) when the average value of the magnetic field difference in a