Abstract: Describes in this paper is a method for measuring 3D position and orientation of endoscope probe inserted in patient’s body by magnetic field. Through deriving particularly three expressions of magnetic field generated respectively by three mutual orthogonal coils, and deriving three expressions of the magnetic induction signals obtained by three mutual orthogonal magnetic field sensors attached in the endoscope at any position and any orientation, a 6D nonlinear equation group （including 3D position and 3 attitude angles） can be constructed. Using Newton Laferson arithmetic and original data obtained from magnetic sensors, the 3D position and orientation （ x, y, z, a, b, c ） of endoscope probe can be determined by solving the 6D equation group. Then, displaying the position of the endoscope probe in the 3D CT image obtained from CT scanner beforehand, it is possible to realize harmless 3D localization and navigation of probe in endoscope diagnosis.