The invention discloses a magnetization and demagnetization method for a spacecraft. The method comprises a magnetization step, a spacecraft testing step and a demagnetization step, wherein a tested spacecraft is demagnetized according to three directions of a three-dimensional rectangular coordinate respectively; each demagnetization process is realized through introducing alternating current into a coil; the frequency of the alternating current is below 1 Hz and the amplitude is gradually attenuated; the maximum magnetic induction strength is not greater than 5 mT; the amplitude is attenuated to the value which is not greater than 1 percent of the maximum magnetic induction strength; and the attenuation is performed in a straight mode or exponential mode. According to the magnetization and demagnetization method for the spacecraft, the anti-magnetic pollution capacity of the spacecraft can be learnt by measuring magnetic field and magnetic moment parameters before and after magnetization of the spacecraft. In addition, in the demagnetization step, residual magnetism caused by magnetic saturation of a soft magnetic material can be removed without adding any extra load or damage to the spacecraft, so that the magnetic index of the spacecraft can be effectively improved.