Magnetic particle imaging (MPI) is an emerging human body functional layer scanning imaging technology that uses biofunctionalized superparamagnetic nanoparticles as tracers. It typically requires the construction of a field-free point / line based on a gradient field and spatial scanning of it to achieve tracer localization. Its spatial resolution is proportional to the gradient field strength. However, high-strength gradient fields need large-volume electro / permanent magnets to construct, making them unable to be used in clinical requirements like minimally invasive lymph node surgery for localization. This study, without using a gradient localization field, proposes a narrow-band magnetic nanoparticle depth positioning theory based on Langevin functions and calculations of the spatial distribution of excitation-magnetization fields. It derives the functional relationship among the magnetic responses produced by magnetic nanoparticles at different depths and the spatial azimuthal angle. A half-peak width-distance detection and true concentration analysis model is formulated. Furthermore, a magnetic particle depth layer scanner (a non-gradient one-dimensional magnetic particle imager) is developed. The vitro experimental measurements show that its spatial positioning resolution is 15 mm with an error of 5. 21% , and the concentration model restoration error is 2. 61% . Compared with the approved European Sentimag static magnetic field magnetic particle positioning device, it has significantly superior performance and can fully meet innovative clinical application requirements like intraoperative lymph node positioning.