Abstract: While drilling, a magnetic inclinometer should be placed inside the non-magnetic drilling tool to avoid the interference of magnetic fields induced by the magnetization of the ferromagnetic drilling tool. However, only a few theoretical studies focus on the influence and determination of the length of non-magnetic drilling tools.Therefore, with ANSYS, a finite element software, a 3D homogeneous strong static magnetic field was created, and the length for the non-magnetic drilling tools needed by the magnetic inclinometer were simulated, with the influences of inclination angle, azimuth angle, and the thickness and length of ferromagnetic drilling tool, etc. The results show that the critical length of the non-magnetic drilling tool had no obvious relationship with the inclination angle and azimuth angle, however, it had a positive correlation with the thickness and length of the ferromagnetic drilling tool. Based on simulated data, the influence of the inclination angle and azimuth angle on the deviation of the azimuth angle was analyzed. It was found that with a fixed axial interference magnetic field, the deviation of the azimuth angle varied with the change of inclination angles and azimuth angles, which was consistent with field practices. The optimized method and result of non-magnetic drilling tool length can serve as reference and theoretical basis for the length determination of non-magnetic drilling tool for magnetic inclinometer in actual survey practices.