The analysis of the influencing factors constitutes the basis of designing the precise line interval in magnetic

searching. Taking the underwater small object as a magnetic dipole, the authors found the law of the magnetic force attenuation

of the magnetic object. A formula for defining searching line space was put forward based on an organic analysis of the influence

caused by such factors as the magnetic force, signaltonoise of the instrument, geomagnetic change, geomagnetic diurnal

variation, and dynamic working condition.