Abstract: Based on multi-objects magnetic anomaly,respective components transformation formulae were deduced theoretically with FFT approach.Regarding normal geomagnetic field as a constant,its Fourier transformation becomes equal to zero except origin in frequency domain.Therefore,the influence of geomagnetic could be eliminated through setting the value of zero on frequency origin,the corresponding error in component transformation has been analyzed as well as the first grade approximate error of anomalous magnetic field.Applying above-mentioned techniques,the transformation of the total field to the component fields was implemented in the frequency domain after calculating the given total field spectrum.The effectiveness of the suggested techniques has been illustrated by three simulated sphere examples and real magnetic data from a collection of environmental ferro-metallic objects.