Active magnetic field calibration method for measurement while drilling (MWD) directional probe

The invention relates to an active magnetic field calibration method for a measurement while drilling (MWD) directional probe. According to the method, an MWD directional probe active magnetic field calibration instrument is used for calibration, and a high-accuracy fluxgate sensor and an MWD directional probe are arranged on a three-axis non-magnetic calibration rotation table; a computer controls a current module to produce current with certain power, a three-axis square Helmholtz coil is driven to produce a uniform magnetic field in a certain range in a central area to offset an earth magnetic field, and a non-magnetic space is formed in a certain range; the fluxgate sensor and the MWD directional probe detect signals, a data acquisition module acquires the signals, and the signals are transmitted to the computer; and calibration software on the computer are used for calculation and comparison to calibrate whether the current MWD directional probe has the qualification that the MWD can descend into the well to work normally. The method has the advantages of quickness, accuracy and stability.