The invention discloses a blasting displacement measuring method and a magnetic target device for measurement. A magnetic target device electrified intermittently is put in an auxiliary hole. After the magnetic target device is electrified, the magnetic target device will generate a local magnetic field at the placement position to disturb the geomagnetic field value at the placement position of amagnetic target, and an interference field will be formed around the magnetic target. The magnetic field intensity of the current area before and after the placement of the magnetic target is obtained by a high-precision proton magnetometer, and data export and diurnal variation correction are carried out by the preprocessing software of the proton magnetometer. A diurnal variation station is setin the magnetic field area to carry out diurnal variation correction on the magnetic field intensity data of a blasting area, the corrected magnetic field intensity data of the blasting site before and after blasting is obtained, the magnetic anomaly of the blasting area is calculated, and a magnetic anomaly magnetic field intensity contour map is drawn. A large number of closed magnetic field intensity contour lines appear in the magnetic anomaly magnetic field intensity contour map, and the position of the magnetic target is thus determined. The positions of the magnetic target before and after blasting are located, and the blasting displacement is measured and calculated according to the positions of the magnetic target before and after blasting.