The invention provides a power grid line-tracking magnetic guidance method based on orthogonal three-position magnetic detection to solve the prominent problems that existing power grid line-tracking guidance efficiency and accuracy are low, and practical requirements cannot be met. The method includes the steps: firstly, building an orthogonal three-position magnetic detection structure, detecting the magnetic field intensity of each position and acquiring the magnetic line direction and the gradient of a magnetic field according to the magnetic field intensity of each position; building the motion equation of a detection aircraft relative to an inertial coordinate system, and building the power grid line-tracking magnetic guidance method of the aircraft according to the detected magnetic line direction and the detected magnetic field gradient. The method can be used for high-precision terminal guidance of power grid fault detection, and has huge application values for rapid repair of a faulted power grid.